Extensible Messaging and Presence Protocol
The Extensible Messaging and Presence Protocol (XMPP) is a protocol for instant messaging. It is inspired by XML.
It is different to most protocols because it is an open standard. This means that anybody who has a domain name and an internet connection can run their own server. Most of the software and the clients are open source.
Other software such as Google Talk and the Gizmo Project use the XMPP protocol. It has been installed on thousands of servers across the internet. There are over ten-million users who use software based on the protocol. [1]