GNU Go is a free program that plays the game of Go.

Go is an ancient game that originated in China, with a definite history of over 3000 years, although there are historians who say that the game was invented more than 4000 years ago. Its name comes from the Japanese name Igo, which means “surrounding boardgame”.

In this game, each player tries to exert more influence on territory than her opponent, using threats of death, capture, or isolation. Although at heart an abstract strategy game, Go has variously been said to be a symbolic representation of war, colonization, settling a frontier, capturing market share, having a debate or a lively discussion in a specialized language, and probably many other concrete situations. Go has always been one of the most played games in the world. Worldwide competitions can make a top player a millionaire.

http://appshopper.com/games/gnu-go