Eggdrop

The world's most popular open source IRC bot, designed for flexibility and ease of use. Eggdrop is freely distributable under the GPL. It was originally developed by Robey Pointer but he no longer works on it.

Eggdrop is designed to run on Linux, *BSD, SunOs, Windows, Mac OS X and other platforms. It is extendable with Tcl scripts and/or C modules. It supports Undernet, DALnet, EFnet, IRCnet, and QuakeNet. It can form botnets and share partylines and userfiles between bots.