Jitsi (formerly SIP Communicator) is an audio/video and chat communicator
that supports protocols such as SIP, XMPP/Jabber, AIM/ICQ, Windows Live,
Yahoo! and many other useful features.

Jitsi is Open Source / Free Software, and is available under the terms of
the LGPL (version 2.1).

WWW: https://jitsi.org/