Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is not a
complete chess program, but requires some UCI compatible GUI (like XBoard with
PolyGlot, eboard, Arena, Sigma Chess, Shredder, Chess Partner or Fritz) in
order to be used comfortably. Read the documentation for your GUI of choice for
information about how to use Stockfish with your GUI.