Jabber/XMPP instant messaging server, written in Erlang/OTP, licensed under GPLv2 (Free and Open Source). Among other features, ejabberd is cross-platform, fault-tolerant, clusterable and modular.
"This article introduces this new concept and explains how to build a distributed event-based infrastructure for social networking. The example application that illustrate this article is a distributed Twitter-like microblogging platform."