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.
Mx3bot is a MySQL based IRC robot, using Tcl for commands, supporting user and channel management, as well as ability to connect to multiple servers at a time.
Nebula: A small and lean IRC client written for motif/lesstif. Small system requirements, speed, portability, security and a clean GUI are its strong points.
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