I am one of the people who occasionally does a Mac build of the current (CVS) version.
Currently a client isn\'t being made public because it would require changes to the Molecular Blue server which everyone is using. The server-side changes have been taken care of in the current pre-CrystalBlue version and I believe that the hope is for a Mac version alongside the Crystal Blue release.
One of the original problems with the Mac version was that the Crystalspace engine ran into performance trouble on the Mac (around late 2002), but that seems to have been avoided since then (either by Apple or CS, I don\'t remember)
Oh, and Keitac2000: die a flaming, horrible death
