Jitsi: SIP Communicator
Jitsi (previously SIP Communicator) is an audio/video and chat communicator that supports protocols such as SIP, XMPP/Jabber, AIM/ICQ, Windows Live, Yahoo!, Bonjour and many other useful features. Jitsi is Open Source / Free Software, and is available under the terms of the LGPL.
The application is developed (mostly) in Java and basd on OSGi.
http://www.jitsi.org/
