A simple chat protocol I and some friends at Lysator developed.
Since the inital developements there have been at least
two 'pure' servers, and a some expanded ones. The currently
recommended version is socktroll.py (in the package socktroll-py)
Socktroll-py also contains an updated version of the GTK client.
For simple client hacking see blamlib
socktroll-py-0.0.3 Contains a bot, an GTK based client and the most advanced server yet.
bzr repository for socktroll, ruby (the original)
For all, License: GPL v3 or newer.