No fuss. Just the classic game of Reversi against an AI player.
Download Desdemona __VERSION__ (0.25 MB disk image). This is a Universal Binary, and should run on Mac OS X 10.3.9 and later.
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The AI beats it creator most of the time at the default level. (But stronger and weaker settings are available.) No opening- or end-game database is used, so it is doubtful that it will perform well against strong players.
Desdemona defaults to using the classic 8x8 board but supports board sizes from 4x4 up to 14x14. Unlimited undo is available should you need it.