libircclient is a small but powerful library, which implements client-server IRC protocol. It has all features needed to create your own IRC client or bot, including multi-threading support, sync and async interfaces, CTCP/DCC support, colors, SSL connections and so on.
psyBNC is an easy-to-use, multi-user, permanent IRC-Bouncer with many features. Some of its features include symmetric ciphering of talk and connections (Blowfish and IDEA) It compiles on Linux, FreeBSD, SunOs and Solaris.
Thabot is an alternative IRC bot for channel administration, developed by french people, written in C and working on several platforms including Windows and un*x systems. Its use is very simple, quick, with level and dynamic level user access, and more t
nwIRC is a small console IRC client for Unix systems. It works without third-party libraries and has been tested on Free/Net/OpenBSD, Darwin, Solaris, HP-UX, OSF1/Tru64, IRIX, AIX, Linux and Cygwin. Key features are multiserver/IPv6/DCC/modules support