BitchX is an IRC client based on ircII/EPIC4. It includes many features that are usually relegated to scripts such as CDCC and flood protection -- you can just start it and go. Development was on hiatus for a while but is now resuming.
IRCBNX Chatterbot is a moderation IRC bot written in C++ and based on the original Battle.net text gateway bot BNX Chatterbot. Like the original, it features a rule-based response system, an access system, and several moderation features.
BBot is a GNU GPL IRC bot for everything from preventing spam to just plain old welcome bots. BBot includes modules to handle factoids, away statuses, do math and more. Writing custom code for BBot is easy, and the more, the better.
Java IRC Bot is a Java framework for writing IRC bots quickly and easily. Its features include an event-driven architecture to handle common IRC events, flood protection, DCC resuming support, ident support, and more.
Z is a security service for IRC networks written in perl, originally based on BotServ. Z is designed to prevent flood and spambots from attacking a network.