http://linux.duke.edu/projects/kibot/
Kibot is a python-based IRC bot written to be cleanly and robustly modular, powerful and flexible. It has a rich permissions framework, and writing modules/commands for it is ridiculously simple.
Kibot is intended to be fun, helpful, and easy to tweak to meet your needs. While it does implement rather thorough security and permissions concepts, it is not intended to play a primarily combative role. If you want to take over channels or protect your channel from serious attacks, use another bot. If you've ever described yourself as 1337, use another bot. If you need a fun, helpful bot for a friendly channel, kibot may be the bot for you!
People keep asking how you pronounce kibot. You should apply the same linguistic principles you use to pronounce LaTeX, MySQL, and baba ganoush. Seriously, I don't care. I originally found the name amusing because Ki is a somewhat uncommon spelling of Chi or Qi. Most people pronounce it KI-bot (like eyedrop).