Kiwi IRC - A hand-crafted IRC client that you can enjoy. Designed to be used easily and freely.
HexChat - HexChat is a fork of XChat with bug fixes and new features.
Colloquy - Traditionally, chat clients on the Mac have been anything but glamorous.
irssi - Irssi is a terminal based IRC client for UNIX systems.
Terminal on FB Messenger - Take control of your terminal through Facebook Messenger
KVIrc - KVIrc is a free portable IRC client based on the excellent Qt GUI toolkit.