Lucky Bot is a fully extendable IRC Bot written in python. It has a nice object oriented API, which makes creating plugins very easy. You can run LuckyBot in console or GUI mode, but in the GUI you can change your settings very easy, enable/disable plugins on runtime etc.
The goal is to support all main operating systems, but the main OS is Linux. It also uses the PyGTK ui lib.
Want to help developing LuckyBot? You can always send in your custom created plugins to me, I will add them to the repository. :) You could also report bugs, or submit your patches for things you think could be improved. You can also create your own branch.