Ubuntu Trusty Internet
Internet applications enable you to make full use of your Internet connection. Web browsers, Email clients, Instant Messengers, and more are included in this category.
Due to trademark and other restrictions of Mozilla products, the Debian project has created versions of the (otherwise free) software that have been stripped of the non-free trademarks and proprietary components. See here and the Debian wiki for more information. To install them, use a package manager to add the Debian repository for your country ( e.g. deb http://ftp.us.debian.org/debian unstable main ) temporarily while installing the software. Then install the software package using the package manager or from the command line:
- IceWeasel replaces the Firefox web browser (sudo apt-get install -t iceweasel) and is now highly recommended instead of Firefox.
- IceDove replaces the Thunderbird email, newsreader, and calendaring client (sudo apt-get install -t icedove).
- IceOwl replaces the Sunbird standalone calendaring client (sudo apt-get install -t iceowl).
- After installation of the individual package, it is best to disable the Debian repository so it does not interfere with the (K)Ubuntu repositories.
- A user that is interested in the philosophy of free software that Iceweasel symbolises may wish to consider a full Debian OS installation (of which (K)Ubuntu is a fork) instead of (K)Ubuntu.
Mozilla Firefox is the ubiquitous web browser. Originally based on open source components, it is trademarked and cannot be altered or re-distributed with any change that involves the name or trademarks. In addition, as of May 2014 proprietary components have been added to Firefox and new bugs in recent versions can cause improper shutdown and OS freezes. Further, the Mozilla company's willingness to indulge in political activism now may pose a security risk from politically motivated coders. For these reasons and others, many users recommend using IceWeasel instead. To install Firefox:
sudo apt-get install firefox
The Firefox web browser supports a wide variety of third-party add-ons, extensions, and plug-ins. They are referred to as "plug-ins" in this guide (the original term) but many are found and configured under the "extensions" or "add-ons" tabs in Firefox (once they are installed).
- Firefox -> Tools -> Add-ons -> Extensions (or Plug-ins)
Adblock Plus plug-in (block ads in a web page)
Adblock Plus blocks ads that appear in web pages. It is an important tool to limit tracking and undesirable website elements, as well. You can subscribe to a free filter service, and can add to the block list individual ads and website elements with a single click.
sudo apt-get install xul-ext-adblock-plus
- You can also add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> AdBlock Plus. (This method will also ensure that automatic updates are installed by Firefox.)
- Recent versions of Adblock Plus allow the display of a large number of "partner" ads unless you disable this undesirable behavior:
- Firefox -> Tools -> Add-ons -> Adblock Plus -> Preferences -> Filter preferences... -> Allow some non-intrusive advertising (unticked)
Because Adblock Plus appears to now be creating holes in its own blocking service, it is probably worthwhile to stop automatic updates and only update Adblock Plus selectively (in case the developers in the future decide to create even more holes in the plug-in's blocking capability without the corresponding option to disable the behavior).
NoScript plug-in (controls scripts)
The NoScript plugin is considered one of the most important security measures for browsing the Internet. Most viruses and trojans gain access to computers from the Internet through scripts. This plugin allows you to choose which scripts to allow and blocks the rest.
- Add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> NoScript. (This method will also ensure that automatic updates are installed by Firefox.)
- NoScript has a long of websites on its "whitelist." It is important to review this list and remove the websites for which you don't wish to automatically allow scripts (I remove them all).
- Firefox -> Tools -> Add-ons -> NoScript -> Preferences -> Whitelist
- A large number of websites use multiple locations/URLs to assemble their webpage content, a process which is blocked by NoScript's ABE (Application Boundaries Enforcer) function. I have found it necessary to disable ABE in order for most of my websites to function correctly.
- Firefox -> Tools -> Add-ons -> NoScript -> Preferences -> Advanced -> ABE -> Enable ABE (unticked)
- Many websites now use aggressive pop-ups to place advertising in front of the actual content. While NoScript can block these ads, there will be a "placeholder" still blocking the content unless you turn off the placeholders:
- Firefox -> Tools -> Add-ons -> NoScript -> Preferences -> Embeddings -> Show placeholder icon (unticked)
- Most websites use scripting extensively these days, so that you may need to "Allow" a website in NoScript. To block the individual undesirable elements of the website, use AdBlock Plus.
Bookmark Favicon Changer plug-in
In the newest versions of Firefox, there are some bugs regarding the Favicons (the small icons that appear in the address bar) and the Bookmark icons. This plug-in will restore the icons that get erased (leaving a blank dotted box) or allow you to choose your own Favicons / Bookmark icons.
- Add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> Bookmark Favicon. (This method will also ensure that automatic updates are installed by Firefox.)
RefreshBlocker plug-in (prevents redirects)
RefreshBlocker allows the user to decide which websites (and pages) will be allowed to redirect (based on META tags within the webpage). Although Firefox (as of version 3.5) blocks all directs by default, the behavior is not customizable; it is therefore preferable to turn off the Firefox redirect control and use RefreshBlocker instead.
- Add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> RefreshBlocker. (This method will also ensure that automatic updates are installed by Firefox.)
- Turn off the Firefox automatic redirect blocker:
- Firefox -> Enter about:config in the browser location bar -> right-click on "accessibility:blockautorefresh" -> Toggle to change the value from true to false
Video DownloadHelper plug-in for Firefox
The Video DownloadHelper plugin allows the download of videos (including Flash videos) from sites like YouTube.
- You can add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> Video DownloadHelper. (This method will also ensure that automatic updates are installed by Firefox.)
Hide Tab Bar With One Tab plug-in
In Firefox v. 23 and later, the ability to hide tabs has been disabled. This plugin restores the ability to hide tabs if only one tab is open, restoring the function to hide tabs during normal browsing.
- You can add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> Hide Tab Bar With One Tab. (This method will also ensure that automatic updates are installed by Firefox.)
User Agent Switcher plug-in for Firefox
The User Agent Switcher plugin allows a browser to masquerade as another browser, allowing browser-specific content to be displayed (most of the time). In the past there were a few old web apps that ran only on IE (and if one is encountered this plug-in may still be useful). Now that Firefox is the world's leading web browser, however, this plug-in should no longer be necessary for the average user.
- A user agent string also identifies your OS. Users of an uncommonly used (and easily identifiable) OS may wish to protect their privacy and not identify their OS correctly; for these users, User Agent Switcher is valuable for privacy reasons. Some users, for example, may wish to identify their very specialised OS as Debian or Ubuntu instead.
- You can add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> User Agent Switcher. (This method will also ensure that automatic updates are installed by Firefox.)
- To use this add-on, the settings for Firefox must be changed prior to usage:
- Firefox -> about:config -> Search: useragent -> general.useragent.enable_overrides -> Toggle (so that the value is true) -> Restart Firefox
Lightbeam (website crosslink visualization)
Lightbeam is a Firefox plug-in that is able to display the links on a website (to which you are connected) while browsing, giving you an indication of who can see your browsing habits at that moment.
- You can add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Search All Add-ons -> Lightbeam. (This method will also ensure that automatic updates are installed by Firefox.)
Privacy Badger (tracking management)
Privacy Badger is a Firefox plug-in sponsored by the Electronic Frontier Foundation. Currently in alpha stage, it blocks many tracking mechanisms more stringently than the native Firefox mechanisms. Install the .xpi add-on from the website.
Unplug Download Management
The UnPlug add-on lets you save video and audio which is embedded on a webpage.
- You can add this extension from Firefox -> Tools -> Add-ons -> Get Add-ons -> Browse All Add-ons. (This method will also ensure that automatic updates are installed by Firefox.)
Lucifox (eBook reader extension)
Lucifox (Lucidor for Firefox) enables e-books to be read and e-book catalogs to be browsed in a Firefox window.
- To install, go to the website and click "Download Now."
Java Runtime Environment (JRE) for Firefox plug-in
- The IcedTea Plugin allows browsers to execute Java applets. The default icedtea-plugin package points to the icedtea-6-plugin package. Install:
sudo apt-get install icedtea-plugin
- Alternatively, install the IcedTea Plugin for version 7:
sudo apt-get install icedtea-7-plugin
- This package may need to be installed to run Java in Firefox, even if the Java Runtime Environment (JRE) is installed using ubuntu-restricted-extras, when installing OpenOffice, or installing the Java enviroment manually.
sudo apt-get install default-jre icedtea-plugin
Note: You must accept the license to use this product.
Adobe Acrobat Reader for Firefox Plug-in
This plugin is allows you to view Adobe Acrobat (PDF) files within the Firefox browser.
- Read Add Extra Repositories and enable the Oneiric partner repository:
deb http://archive.canonical.com/ubuntu Oneiric partner
- then install Adobe Reader:
sudo apt-get install acroread
- Alternatively, this plugin is also available from the Medibuntu repository. Add the Medibuntu repository to your repository list:
deb http://packages.medibuntu.org/ Oneiric free non-free
- then install:
sudo apt-get install acroread mozilla-acroread acroread-plugins acroread-fonts
Adobe Flash Player for Firefox Plug-in
To install the official Adobe Flash plugin (Flash 10) for Firefox:
sudo apt-get install adobe-flashplugin
Gnash Plug-in (Open source Flash Player replacement)
Gnash is available in a 64-bit version as well as a 32-bit version. It is the open source replacement for Adobe Flashplayer.
sudo apt-get install gnash
After installing, change your web browser's Preferences -> Applications so that SWF and SPL files use Gnash.
VLC plug-in for Firefox
This package allows the popular VLC player to play media within the Firefox browser.
sudo apt-get install mozilla-plugin-vlc
Gecko MediaPlayer Plug-in for Firefox
Gecko MediaPlayer is a browser plugin for all Gecko-based browsers (Firefox, SeaMonkey, IceApe, Opera) that allows Mplayer to play multimedia within the browser. Install:
sudo apt-get install gecko-mediaplayer
An alternative is to use the mplayer plugin for Firefox. Install:
sudo apt-get install mozilla-mplayer
Kaffeine Plug-in for Firefox
This package allows the Kaffeine media player (often used in KDE-based desktops) to play multimedia within the Firefox browser.
sudo apt-get install kaffeine-mozilla
Helix player plug-in for Firefox
This package installs the Helix player (the open source player that plays Real Player content in Linux) as well as the plugin that plays RealMedia within the Firefox browser.
sudo apt-get install mozilla-helix-player
Moonlight plugin for Firefox
Moonlight is part of the Mono project that is an open source implementation of Silverlight (the Microsoft multimedia presentation platform). It is based on FFMpeg. It is made to work best with the Firefox web browser, as a plugin (but also works with other Mozilla browsers). It is available as a plugin for mozilla-based browsers:
sudo apt-get install moonlight-plugin-mozilla
- Netflix under Moonlight
- Netflix streaming requires both the capabilities of Silverlight 2.0 and Digital Rights Management modules. Although the current version of Moonlight 2.0 will run most Silverlight content (including Netflix content), Netflix has not yet released Digital Rights Management modules for Linux. Please contact Netflix directly for further information or sign a petition.
FireFTP for Firefox
FireFTP is a Firefox extension for FTP transfers.
Turn off browser bar drop-down list in Firefox
This is the most frequently asked problem regarding Firefox. To turn off the location browser bar drop-down list (and therefore not show your browsing history):
- Firefox -> about:config (in the location browser bar) -> browser.urlbar.maxRichResults -> right-click -> Modify -> set value to 0
Turn off SSL certificate name in address bar
In newer versions of firefox, the validity of the SSL certificate associated with a website is displayed as a color-coded background to the Favicon (the small icon displayed in the address bar). However, Firefox currently also displays the name of the site issuing the SSL certificate, which can be annoying, since for most sites this is a duplicate of the domain name (which then gets displayed twice in the address bar). To turn off this behavior:
- Firefox -> about:config (in the location browser bar) -> browser.identity.ssl_domain_display -> right-click -> Modify -> set value to 0
View Firefox cache
In a new window/tab, enter about:cache in the Firefox address bar. You can view and save individual elements (from all open windows/tabs) in the cache from there.
The GNU project also maintains a version of Mozilla Firefox that is free of trademarks and branding, called GNUZilla IceCat. .deb packages for (K)Ubuntu can be downloaded and installed through the GNUzilla PPA repositories.
Opera is a proprietary browser and internet suite (currently free on PCs) also used in some mobile devices and gaming consoles. It includes email, an address book, IRC chat, integrated BitTorrent, and webfeeds. A limited number of plugins are also available. Download from the website and follow the instructions or install from the Opera repository:
echo "deb http://deb.opera.com/opera/ stable non-free" | sudo tee /etc/apt/sources.list.d/opera.list wget -O - http://deb.opera.com/archive.key | sudo apt-key add - sudo apt-get install opera
Chromium is the open source browser on which Google Chrome is based. It does not include the undesirable user tracking mechanisms of Google Chrome or the Google logos (and is therefore recommended by many users instead of Chrome).
sudo apt-get install chromium-browser
Google Chrome is Google's proprietary web browser. Based on the open-source Chromium browser, Google adds the Google name and logo, an auto-updater system called GoogleUpdate, RLZ (a user-tracking mechanism), and other Google add-ons. To use this instead of Chromium, download and install the .deb package here.
MultiGet is a GTK-based free-standing download manager utility.
sudo apt-get install multiget
- Here is a sample list of free Usenet servers.
sudo apt-get install pan
Evolution is the default Gnome-based email client in Ubuntu. If not installed:
sudo apt-get install evolution
Evolution and PGP
Mozilla Thunderbird is a licensed and trademarked free open-source email client that is compatible with Firefox. Install:
sudo apt-get install thunderbird
Lightning calendar extension
sudo apt-get install xul-ext-lightning
Enigmail is an add-on to Thunderbird that allows you to easily encrypt your email using OpenPGP, which is included in the kernel by default. It also allows you to create and manage the encryption keys. Go the website and click "Download Now". (64-bit versions are found here.) Install:
- Thunderbird -> Tools -> Add-ons -> Install -> select downloaded file
sudo apt-get install enigmail
- Also see these tips for instructions on setting up e-mail with PGP encryption.
Miniminize to System Tray
MinimizeToTray revived is a valuable plugin/add-on/extension, IMO. It allows Thunderbird to be minimized to the System Tray instead of to the Taskbar. This allows Thunderbird to run discreetly in the background, checking for new mail and calendar events (e.g. through the Lightning extension). The same plugin/add-on/extension also is available for Firefox. Install:
- Thunderbird -> Tools -> Add-ons -> Get Add-ons -> Browse all add-ons (takes you to an external webpage) -> search for add-ons: MinimizeToTray revived -> + Add to Thunderbird -> Install Now -> Restart Thunderbird
New Mail Icon for Thunderbird
New Mail Icon is an experimental tray add-on which notifies you of new mail. (Note: If you leave Thunderbird running minimized to the System Tray (with the MinimizeToTray add-on, for example), it has a built-in "new message" notifier already, so that this add-on would not be necessary in such a situation.) Download from the website. Install:
- Thunderbird -> Tools -> Add-ons -> Install -> select downloaded file
KMail (Kontact Mail) is the default email client included with Kontact in KDE (Kubuntu). Kontact includes email, an address book, a calendar, reminders, pop-up notes, a link to the Akregator News/RSS reader, time-tracking, and more. Install:
sudo apt-get install kontact
sudo apt-get install akregator
Install java and in order to use the internal browser, install the packages xulrunner and firefox:
sudo apt-get install sun-java6-jre firefox xulrunner
Change to your "opt" directory:
Download the zip-archive into your opt directory:
sudo wget http://downloads.sourceforge.net/rssowl/rssowl-2.0.6.linux.zip
Extract the archive and remove the extracted file:
sudo unzip ./rssowl-2.0.6.linux.zip && sudo rm ./rssowl-2.0.6.linux.zip
Make a startscript:
sudo gedit /usr/bin/runRSSOwl.sh
add the following lines to your startscript file /usr/bin/runRSSOwl.sh and save it afterwards.
#!/bin/bash cd /opt/rssowl ./RSSOwl
Make the startscript executable:
sudo chmod u+x /usr/bin/runRSSOwl.sh
To start RSSOwl:
Empathy is an open source IM application. It is the default in the Ubuntu (Gnome) desktop. You can access multiple services with it. If not already installed, you can install it:
sudo apt-get install empathy
Pidgin is an open source IM application. It is the previous default in the Ubuntu (Gnome) desktop. You can access multiple services with it.
sudo apt-get install pidgin
Kopete is the default Instant Messenger application for Kubuntu. You can access multiple services with it. Install:
sudo apt-get install kopete
Additional styles for Kopete are available from KDE-look. Install from:
- Kopete -> Settings -> Configure -> Chat Window -> Style -> Get New...
GoogleTalk on Kopete
Konversation (IRC client)
sudo apt-get install konversation
XChat (IRC client)
XChat is a cross-platform IRC client that allows DCC downloads and scripts. Install:
sudo apt-get install xchat
- or a Gnome-integrated version:
sudo apt-get install xchat-gnome
aMSN is an MSN Messenger utility that functions like the original client. It is alternative to Pidgin for MSN users. Install it:
sudo apt-get install amsn
To enable Drag-and-Drop capabilities to aMSN for easy file transfer see Ubuntu Geek.
sudo apt-get install emesene
Filezilla is the ubiquitous free open-source FTP client and server for all platforms.
sudo apt-get install filezilla
Filesharing / P2P
- Do not share copyrighted material or content that is otherwise illegal to share.
- In an era of increasing censorship, spying, and surveillance using Deep Packet Inspection, encryption has become an essential componenet of data transfer. Look for clients that allow data encyrption.
- It is possible to use PeerGuardian 2 with several clients. This service attempts to monitor and filter IP addresses known for censorship, spying, or provision of false or malicious data to this type of Internet service. Look for clients that are able to use this service.
Azureus is a Java-based BitTorrent client.
sudo apt-get install azureus
QBitTorrent is a PyQT-based BitTorrent Client that is based on the uTorrent model.
sudo apt-get install qBittorrent
Transmission (BitTorrent Client)
sudo apt-get install transmission
Deluge is a GTK-based BitTorrent client, with plugins and a server package / daemon available. Install the client:
sudo apt-get install deluge-torrent
or the GTK-based interface:
sudo apt-get install deluge-gtk
- The server daemon and web interface (for server functions) can be installed:
sudo apt-get install deluged deluge-web
Bittornado (BitTorrent Client)
BitTornado is a KDE-compatible BitTorrent client. Install:
sudo apt-get bittornado bittornado-gui
Torrentflux (P2P client and server)
TorrentFlux is a PHP based BitTorrent controller that runs on a web server (using a MySQL database with the mysql-server package for server functions or the mysql-client for client functions) and uses a web interface that can be accessed remotely (e.g. http://localhost/torrentflux). This makes it ideal for seedbox purposes. It uses the BitTornado client for downloads. Install:
sudo apt-get install torrentflux
Apollon (P2P Filesharing)
Apollon is an older (now relatively obsolete) BitTorrent client that uses the Gift network (Gnutella, etc.). It uses plugins for compatibility with multiple networks. Obtain the packages from the Debian Etch archives for apollon and gift.
MLDonkey (P2P eMule/eDonkey2000)
MLDonkey is a P2P file sharing program (and network) that is able to use different network protocols. To install the MLDonkey core server, follow these instructions.
MLDonkey GUI frontends
- Install the Gnome GUI frontend for MLDonkey:
sudo apt-get install mldonkey-gui
sudo apt-get install kmldonkey
Opentracker (Torrent tracker)
Opentracker is the most widely used torrent tracker software. It can be used within a private organisation or as a public service to track freely-available torrents. Download (through CVS) and installation instructions are at the website.
Videoconferencing and VoIP
Videoconferencing and voice over Internet (VoIP) applications are merging into integrated applications. Most of these applications now allow placing calls to non-Internet based telephones for a small fee.
Formerly known as Gnomemeeting, Ekiga is a SIP compliant fully functional open source integrated VoIP and videoconferencing program.
sudo apt-get install ekiga
- Install pre-requisites:
sudo apt-get install libqt4-dbus libqt4-network libqt4-xml
- To get the most recent version, download and install the 32-bit version:
wget -O skype-ubuntu-current_i386.deb http://www.skype.com/go/getskype-linux-beta-ubuntu-32 sudo dpkg -i skype-ubuntu-current_i386.deb sudo rm skype-ubuntu-current_i386.deb
wget -O skype-ubuntu-current_i386.deb http://download.skype.com/linux/skype-ubuntu-precise_220.127.116.11-1_i386.deb sudo dpkg -i skype-ubuntu-current_i386.deb sudo rm skype-ubuntu-current_i386.deb
- In the past. some users have noted that they cannot get their microphone inputs to work with any version later than 18.104.22.168. They installed:
wget -O skype-ubuntu-current_i386.deb http://download.skype.com/linux/skype-debian_22.214.171.124-1_i386.deb sudo dpkg -i skype-ubuntu-current_i386.deb sudo rm skype-ubuntu-current_i386.deb
wget -O skype-ubuntu-current_amd64.deb http://download.skype.com/linux/skype-ubuntu-intrepid_126.96.36.199-1_amd64.deb sudo dpkg -i skype-ubuntu-current_amd64.deb sudo rm skype-ubuntu-current_amd64.deb
How to install Skype on a 64-bit system
The current version of Skype for 64-bit systems is a masqueraded 32-bit module. To use on a 64-bit system you might still need to install the needed packages:
sudo apt-get install ia32-libs lib32asound2 libqt4-core libqt4-gui
- Then download and install the current Skype .deb package from the Skype website:
wget -O skype_ubuntu-current_amd64.deb http://www.skype.com/go/getskype-linux-beta-ubuntu-64 sudo dpkg -i skype-ubuntu-current_amd64.deb sudo rm skype-ubuntu-current_amd64.deb
- If the 64-bit version doesn't work for you, use the 32-bit version (or see above for the most recent version):
wget -O skype-ubuntu-current_i386.deb http://www.skype.com/go/getskype-linux-beta-ubuntu-32 sudo dpkg -i --force-architecture skype-ubuntu-current_i386.deb sudo rm skype-ubuntu-current_i386.deb
Installing Skype repository
It is possible to install Skype by adding the repository and installing from there. This has an advantage of maintaining updates automatically.
- Install the respository security key. (This requires an open port 11371 in your firewall for the keyserver.)
sudo apt-key adv --keyserver pgp.mit.edu --recv-keys 0xd66b746e
- Add the Skype repository, update, and install Skype:
echo "deb http://download.skype.com/linux/repos/debian/ stable non-free" | sudo tee -a /etc/apt/sources.list > /dev/null sudo apt-get update sudo apt-get install skype
Wengophone is an integrated VoIP and videoconferencing client available on many platforms. Wengophone was initially an open-source GPL-licensed package ('Wengophone Classic'). Both the Classic version (available as a .deb file) and the current proprietary binary version are available from the website. Wengophone Classic has now been rebranded as QuteCom, however. To install the current version as an Ubuntu/Kubuntu package, see these instructions.
- Download and install the older Wengophone Classic version (.deb package):
wget http://download.wengo.com/wengophone/rc/wengophone-0.958m-1.i386.deb dpkg -i --force-architecture wengophone-0.958m-1.i386.deb
Gizmo5 is an Internet soft-phone application, similar to Skype, that uses the SIP protocol. Install (.deb package):
wget http://download.gizmo5.com/GizmoDownload/gizmo-project_188.8.131.52_libstdc++6_i386.deb dpkg -i --force-architecture gizmo-project_184.108.40.206_libstdc++6_i386.deb
Asterisk VoIP PBX system
Asterisk is an enterprise-grade, free open source PBX and telephony system for VoIP.
sudo apt-get install asterisk
Kiax is an LGPL-licensed open source IAX (Inter-Asterisk eXchange) application. It is used for making VoIP calls from an Asterisk PBX. The current version must be installed from source files. See the website for download and installation instructions, or see this Ubuntu Launchpad site.
OpenSIPS / OpenSER (SIP server)
OpenSIPS is an open-source SIP server that allows connections to be made through the Internet for VoIP, IM, and other communications protocols. While there are many public SIP servers, these are subject to spoofing and other "impersonation" problems. A company may wish to host its own SIP server to avoid the problems inherent in public services whose trustworthiness can not be determined. OpenSIPS is the successor to OpenSER (which is the version in the repositories). Install OpenSER 1.3.2 from the repositories:
sudo apt-get install openser
Alternately, the newest version of OpenSIPS can be downloaded as a .deb package from the website and installed. Installation and usage instructions are on the website.
Telepathy is a flexible, modular communications framework that enables real-time VoIP/chat communication via pluggable protocol backends (for protocols such as Jabber/XMPP/Google Talk/Jingle, link-local XMPP, SIP, MSN, Yahoo/AIM and IRC). Telepathy is a communications service that can be simultaneously accessed by many client applications (primarily Empathy), using Qt 4, Glib, and GtK libraries. Currently a version for the GNOME desktop (telepathy-gnome) is available. Install:
sudo apt-get install telepathy-gnome
Web meeting software allows video conferencing among many clients, with one server as host.
BigBlueButton is a free open source chat/video/audio and desktop sharing platform similar to GoToMeeting, WebEx, DimDim and similar products. Developed by GoogleCode, it utilises all open-source modules. A Moodle plugin is also available. See these installation instructions and these additional detailed instructions.
WebHuddle is a free, open source Java-based browser client (and server) for web meetings. To install the server, first install pre-requisites, including Java, JBOSS Application Server, and xvfb.
sudo apt-get sun-java6-jre jbossas4 xvfb
For more details on setting this up in (K)Ubuntu, see this.
TeamViewer is a proprietary cross-platform package that enables up to 25 participants to share a desktop for online meetings and provides a mechanism for users to control a PC's desktop remotely. Presentations can be viewed through most Internet web browsers, as well. A free .deb package can be downloaded here.