GNU Chess is a free software chess engine which plays a full game of chess against a human being or other computer program. The goal of GNU Chess is to serve as a basis for research. It has been used in numerous research contexts.

GNU Chess is free software, licensed under the terms of the GNU General Public License version 3 or any later version, and is maintained by collaborating developers. It's one of the oldest computer chess programs for Unix-based computers and one of the earliest available with full source code. GNU Chess has been ported to many other platforms.

On basic, current computer chess architecture, GNU Chess plays at senior master/weak international master strength (2500+ Elo on simple hardware - Intel Core 2 Duo), without parallel processing, according to the IQ6 test suite.