Jitsi is an audio/video Internet phone and instant messenger written in Java. It supports some of the most popular instant messaging and telephony protocols such as SIP, Jabber/XMPP (and hence Facebook and Google Talk), AIM, ICQ, MSN, Yahoo! Messenger.

Jitsi Instant Messenger has the following features:

• Audio calling
• Video calling
• Desktop streaming
• Audio conference calls
• Call recording
• One-to-one chats
• Multi-user chats
• File transfer
• Integration with Microsoft Outlook and Apple Address Book

REVLY specifically uses the XMPP protocol with Jitsi.