stockfish

Stockfish is a free and open-source chess engine renowned for its strength and broad availability. Released under the GNU General Public License version 3 or later, it communicates with chess graphical user interfaces through the Universal Chess Interface and WinBoard protocols, allowing use with many popular GUI programs.

Development began in the late 2000s as a fork of the Glaurung family of engines and has since evolved into a community-driven project with contributors around the world. The engine is continuously improved by volunteers who work on its search algorithms, evaluation function, and portability across platforms.

Stockfish employs a highly optimized search based on alpha-beta pruning, iterative deepening, and transposition tables, and it supports multi-core and vectorized execution for fast performance. It is designed to run on various architectures and can use endgame tablebases via the Syzygy system. The evaluation component traditionally relied on handcrafted heuristics, but in recent years Stockfish also incorporates neural network based evaluation (NNUE) to enhance accuracy without sacrificing speed.

As a result, Stockfish has been among the strongest chess engines in the world, frequently topping online computer chess rankings and winning or placing highly in major matches and tournaments such as the Top Chess Engine Championship. It is widely used for analysis and as a backend by many chess clients and services, and its open nature has spurred numerous forks and adaptations while remaining under the same GPL license.