Supybot is a robust (it doesn't crash), user friendly (it's easy to configure) and programmer friendly (plugins are extremely easy to write) Python IRC bot. It aims to be an adequate replacement for most existing IRC bots. It includes a very flexible and powerful ACL system for controlling access to commands, as well as more than 50 builtin plugins providing around 400 actual commands.
Limnoria is a project which continues development of Supybot (you can call it a fork) by fixing bugs and adding features (see the list of added features for more details).
Limnoria is tested with Python 2.6, 2.7, 3.2, 3.3, and Pypy. Python 2.5 and older versions are not supported.
If this is your first install, there is an install guide. You will probably be pointed to it if you ask on IRC how to install Limnoria.
If you have any trouble, feel free to swing by #supybot and #limnoria on irc.freenode.net or #supybot at irc.oftc.net (we have a Limnoria there relaying, so either network works) and ask questions. We'll be happy to help wherever we can. And by all means, if you find anything hard to understand or think you know of a better way to do something, please post it on the issue tracker so we can improve the bot!
Only French yet, at #supybot-fr on freenode.