Pigeon is a 64-bit chess engine, written by Stuart Riffle. It runs on Windows and Linux, and will plug into any UCI-compatible chess GUI (like this one).

The latest version is rated about 2000 against humans online, at both ICC and FICS. That's pretty good, you know, for a bird.

When playing against other chess engines, Pigeon has a CCRL 40/4 rating around 1800, which is... somewhat less good. But it always tries very hard.

Full C++ source code is available on GitHub, under the terms of the MIT license, so knock yourself out.

  Download Pigeon 1.5.1