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.
Terminal on FB Messenger - Take control of your terminal through Facebook Messenger
irssi - Irssi is a terminal based IRC client for UNIX systems.
Adium - Adium is a free instant messaging application for Mac OS X that can connect to AIM, MSN, Jabber, Yahoo, and more.
Nettalk - Nettalk is a powerful but easy to use free (open source) IRC-client for Windows.