ejabberd is a Free and Open Source distributed fault-tolerant Jabber server. 
It writen mostly in Erlang. 

The main features of ejabberd is:
	- Works on most of popular platforms: *nix 
	  (tested on Linux, FreeBSD and NetBSD)
	- Distributed
	- Fault-tolerance: 
	- Built-in Multi-User Chat service 
	- Built-in IRC transport 
	- Built-in Publish-Subscribe service 
	- Built-in Jabber Users Directory service based on users vCards 
	- SSL support 
	- Ability to interface with external components (JIT, MSN-t, Yahoo-t, etc) 
	- Migration from jabberd14 is possible 
	- Mostly XMPP-compliant 
	- Support for JEP-0030 (Service Discovery). 
	- Support for JEP-0039 (Statistics Gathering). 
	- Support for xml:lang attribute in many XML elements 

WWW: http://ejabberd.jabberstudio.org/