Stockfish

Stockfish is a chess engine, that is to say a chess AI. It is at the time of this writing the strongest or in general one of the strongest computer chess programs in existence.

A notable feature of Stockfish versus other computer chess engines, which has made it so exceedingly powerful, is the Fishtest worker program. . Users run this program and donate their computer time to have development versions of Stockfish play very large numbers of test games against one another. This is used to measure the effectiveness of proposed changes, allowing the program to grow rapidly in playing strength and letting regressions be weeded out.