HexChat - HexChat is a fork of XChat with bug fixes and new features.
irssi - Irssi is a terminal based IRC client for UNIX systems.
KVIrc - KVIrc is a free portable IRC client based on the excellent Qt GUI toolkit.
Kiwi IRC - A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely.
Quassel IRC - Quassel IRC is a modern, cross-platform, distributed IRC client based on the Qt4 framework.
Chatzilla - Chatzilla is a Web IRC client built on Mozilla, providing users from around the globe to chat with others in a sumptuous and engaging way.