ichiGo 1.0 Beta 1
This is based on an old Chinese board game called Go.
It's a two-player game with three standard boards: 9x9, 13x13 and 19x19. You can perform an unlimited number of undos, and the score window only shows prisoners, not territory.
When each player has passed, the dead groups are removed, and the sum of prisoners and territory is displayed along with the actual score.