A
Mac OS ICQ client, written because the
Mirabilis client sucked rocks at the time. (It might still
suck rocks, but I wouldn't know)
The best ICQ client for any OS. Full stop.
See http://www.gerryicq.com/
It's interesting to note that Gerry managed to get the Carbon version of GICQ running under Mac OS X despite not actually having access to a machine that runs OS X. Unfortunately though, Gerry seems to have lost interest in his client of late, so further updates may be a long time in coming.