Jitsi (previously SIP Communicator) is a cross-platform VOIP, videoconference, desktop sharing and chat client.

Protocols supported include SIP, XMPP/Jabber/Google Talk/Facebook chat, AIM/ICQ, Windows Live, Yahoo! Messenger and Bonjour.

Other features include: Call recording, Call & chat encryption, Noise suppression, Echo cancellation, File transfer, multi-user chat, Desktop streaming, Presence, Conference calls, Integration with Microsoft Outlook and Apple Address Book, Support for LDAP directories, Support for Google Contacts, On-line provisioning, Systray notifications, IPv6 support, Spell checker and many more.

License: LGPL
http://jitsi.org/

This has emerged into Jitsi Meet