Openfire (formerly Wildfire) is an enterprise instant messaging (EIM) server
dual-licensed under the Open Source GPL and commercially. It uses the leading
open protocol for instant messaging, XMPP (also called Jabber). 
Openfire is incredibly easy to setup and administer, but offers rock-solid 
security and performance.

WWW: http://www.igniterealtime.org/projects/openfire/index.jsp