jabber

Jabber is an open XML protocol for the real-time exchange of messages and presence between any two points on the Internet. The first application of Jabber technology is an asynchronous, extensible instant messaging platform, and an IM network that offers functionality similar to legacy IM systems such as AIM, ICQ, MSN, and Yahoo. However, Jabber offers several advantages over legacy IM systems:

• Open — the Jabber protocol is free, open, public, and easily understandable, and multiple open-source implementations exist for Jabber servers, clients, and development libraries.
• Extensible — using the power of XML namespaces, anyone can extend the Jabber protocol for custom functionality; to maintain interoperability, common extensions are managed by the Jabber Software Foundation.
• Decentralized — anyone can run their own Jabber server, enabling individuals and organizations to take control of their IM experience.
• Secure — Any Jabber server may be isolated from the public Jabber network, many server implementations use SSL for client-server communications, and numerous clients support PGP/GPG for end-to-end encryption; more robust security using SASL and session keys is under development.