This page hasn't been updated since 2007, so it's out of date. However, the Macintosh users that we know use an iPad/iPhone for almost all Go playing, so it may be that this page is actually effectively redundant.
Please go to the iOS software page  for current information on this software.
This page describes some Go software for the Mac.
These descriptions were mostly written by dlbond, and are given here with his permission.
The programs described are available via this page .
Goban (includes GnuGo 3.2)Goban is a Mac OS X frontend for GnuGo 3.2. The current version of GnuGo compiles out of the box on OS X, and is probably the strongest program you will find for the Mac.
All normal board sizes and handicaps are supported.
Goban also functions as an internet go client.
Explorer 3.3Explorer 3.3, by Martin Muller, used to be easily the strongest Go playing shareware program for the Classic Mac OS. Its major claim to fame is that it won the World Computer Go Championship in 1989. While its ranking has dropped in recent years, it remains a challenger (see here ).
Explorer allows for the creation of game trees (variations), marking of stones, estimation of score, and can provide hints. It reads .sgf files and even displays the comments. An excellent feature is the 'Text Display', that cites reasons in the form of numerical weights, why a move has been made or has been recommended. E.g.: nobi 159 - to protect to capture 48 - escape by semeai 247 etc. It is very useful for the novice to see what the computer is considering. It helps develop a better understanding of strategy and serves as an introduction to the more common Japanese terms.
Explorer is in black and white, and allows for board sizes of 9x9, 13x13 and
19x19. Explorer has 2 algorithms to play against; Swiss Explorer and
Lookahead (somewhat weaker). It allows the player to be black or white,
and can be set to play against itself. It does take quite a while to think
about its move (even on a PPC), especially when confronted with a ladder,
but I have yet to see Explorer make a pointless move or a serious mistake.
A game can be either 9x9, 13x13 or 19x19. The board is your choice of a few pretty colours and patterns. Lumpy plays quickly. Overall a useful teacher, and an attractive production.