KVIrc is a graphical IRC client for Linux, Unix, Mac OS and Windows. Developed by HelLViS69 - code - hellvis69 @ netsons.org
License: Open Source
Apps available for Mac OS X Windows Linux BSD PortableApps.com
Irssi is an IRC client program for Linux, FreeBSD, Mac OS X and Microsoft Windows. Developed by irssi.org
Apps available for Mac OS X Linux Xfce