Jitsi (formerly SIP Communicator) is an Internet communicator that supports secure audio/video call with two or multiple participants over SIP and XMPP/Jabber. It also supports chatting via other protocols such as  AIM/ICQ, Yahoo! Messenger and Windows Live. Jitsi is the most advanced open source communications too. Jitsi is Open Source / Free Software, and is available under the terms of the LGPL.