GNU Backgammon is the obvious choice.
There's also eXtreme Gammon, which is faster and probably slightly
stronger, but you'll need a Windows emulator to run it on a Mac.
--
Tim Chow tchow-at-alum-dot-mit-dot-edu
The range of our projectiles---even ... the artillery---however great, will
never exceed four of those miles of which as many thousand separate us from
the center of the earth. ---Galileo, Dialogues Concerning Two New Sciences
See http://www.bkgm.com/software.html#macintosh
My recommendation would be gnubg (free, does everything you need it to)
or JavaFibs (also free) if you're going to play on FIBS.
//Walt
You might also look at BGBlitz (www.bgblitz.com) which runs native on
the mac...