JediKnight was a decent IRC client on NS/OS.
Development continued on Mac OS X until 2.1.
Does anyone have JediKnight2.1.dmg.gz kicking around?
Internet Archive, MacUpdate - all point back to the defunct stuffonfire.com domain.
I went to school with Dave (the developer) and we were roommates for a while. JediKnight became Newspeak and is open source and hosted on sourceforge.net:
http://sourceforge.net/projects/newspeak-irc/