ejabberd is a useful, free and open source instant messaging server written in Erlang. ejabberd is cross-platform, distributed, fault-tolerant, and based on open standards to achieve real-time communication (Jabber/XMPP).

Key Features:

Multiplatform
· Works on most popular platforms. Tested on Linux, FreeBSD, NetBSD, Solaris, Mac OS X and Windows NT/2000/XP.

Distributed
· You can run ejabberd on a cluster of machines and all of them will serve one Jabber domain. When you want to expand your Jabber server you can simply add a new cheap node to your cluster. So you dont need to buy an expensive high-end machine to support hundreds of concurrent users.

Fault-tolerant
· The nodes on the ejabberd cluster share some or all tables in the database, so all the information required for a properly working service will be stored permanently on more than one node. If one of the nodes crashes the other nodes will continue working without disruption. You can also add or replace nodes on the fly.

Easy Setup
· ejabberd is built on top of Open Source Erlang/OTP. So you dont need to setup an external database, an external web server, etc because everything is already installed, and ready to run out of the box.
· improved in 1.0.0

Virtual Hosts
· Several Jabber hosts can be hosted on the same ejabberd instance. As simple as adding a new domain name to the list of hosts in the configuration file.

IPv6 Support
· It supports IPv6 both for c2s and s2s.