mrtoms is an IRC bot written in Scala. It supports a very powerful and easy to use plugin system where plugins are compiled to and loaded from jar files. mrtoms comes with a Z-machine interpreter plugin so that games like Zork can be played collaboratively. It also includes an MPD control plugin and others.
Ibid is a multi-protocol, general purpose, instant messaging chat bot written in Python. It aims for a naturalistic interface rather than strict-syntax commands. Ibid understands many protocols, including IRC, Jabber/XMPP/Google Talk, Campfire, NMDC, and SILC. It also interacts over SMTP, HTTP, and various RPC protocols. Ibid aims to make plugins as easy as possible to write. It ships with a large collection of plugins for looking up information, performing conversions, storing factoids, delivering messages, and much more.