Xmpp
Snikket
Be your own instant messaging provider, using open source and open standards.
Prosody IM
A lightweight extensible XMPP server
Verse
An XMPP library for Lua
Scansion
An automated XMPP testing tool.
Riddim
A modular XMPP bot framework
Modern XMPP
A lighthouse for modern XMPP software developers