Shakti is essentially a Chess-style game, in that the object is to force the capture of the opponent's King. But the rules are much easier to learn than Chess, while still maintaining nontrivial strategy.
Shakti Lite is freeware, and may be downloaded from: http://www.strout.net/files/shakti-lite.sea.hqx (250K)
This application requires MacOS 7.0 or later. It will make use of BetterBeep, if you have it.
A Shakti Pro is planned, which will have many more features, and will be available from MindSports. Stay tuned!