A small list of software engine who play GO.
Go engines don''t have a graphical interface so for the best experience you will need one who know how to connect to those engines like GoGui or Drago
GNU Go is a free program that plays the game of Go. GNU Go has played thousands of games on the NNGS Go server. GNU Go 3.8, released February 19, 2009, is the latest stable version. It is portable and known to work well on GNU/Linux, Windows and Mac OS/X systems.