Jitsi (formerly: SIP Communicator)

https://jitsi.org/

Jitsi is an audio/video Internet phone and instant messenger that supports some of the most popular VoIP and instant messaging protocols such as SIP, Jabber, AIM/ICQ, MSN, Yahoo! Messenger, Bonjour and a whole lot of other useful features including:

Features

• Voice and video calls using SIP and XMPP/Jingle (Actually the only XMPP/Jingle Client for Windows I know of)
• Desktop streaming and sharing
• Call encryption with SRTP and ZRTP
• Conference calls - also across accounts (audio so far - video and destop streaming in the works)
• File transfer for XMPP, AIM/ICQ, .NET Messenger Service, Yahoo!
• Direct media connection establishment (P2P) with the ICE protocol
• Instant messaging encryption with Off-the-Record Messaging
• Attended and blind call transfer
• Auto away
• Awto answer
• Auto forward
• Auto re-connect
• Call recording
• Encrypted password storage using a master password
• IPv6 support for SIP and XMPP
• Media relaying with the TURN protocol and Jingle Nodes
• Wideband audio with Skype's SILK, G.722 and Speex
• DTMF with SIP INFO, RTP (RFC 2833 and 4733) and Inband
• DNSSEC

Supported Protocols

• XMPP (Google Talk, LJ Talk, Gizmo5, Facebook Chat, ...)
• SIP
• .NET Messenger Service (commonly known as MSN Messenger or Windows Live Messenger; no multimedia support)
• Bonjour (Apple's implementation of Zeroconf)
• OSCAR (AIM/ICQ/.Mac)
• Yahoo! (only basic chat and file transfers)

Tested Interoperability

• Asterisk (Video and Audio)
• Linphone (Video and Audio)
• Ekiga (Video with additional H264 codecs, Audio)
• Empathy (XMPP/Jingle - without encryption, Video and Audio)
• Google Talk (Video and Audio)

Jitsi (SIP Communicator) supports multiple operating systems, including

• Windows
• Unix-like systems such as Linux, BSD.
• Mac OS X

SIP Communicator is completely Open Source / Free Software, and is freely available under the terms of the GNU Lesser General Public License

Screenshots

Contact List	Call History	Conference Call

Audio/Video Call