ScriptBot is a scriptable IRC bot. Based on PircBot and BSF, it allows to fully customize the bot's behaviour by editing script files in the scripting language of your choice.
Hollaka Hollala is a chatbot engine and IRC bot. The chatbot engine uses a knowledge base organized in an XML file and WordNet for dictionary lookup. The IRC Bot has some WordNet- and Web-based functionality and is hot-extensible through Ruby programs.
XIC is a full featured, cross platform IRC client. There are both graphical and CLI versions planned, as well as various language versions.