XBoard is a graphical user interface chessboard for chess engines under the X Window System.

XBoard/WinBoard supports this protocol (and its dialects USI and UCCI, which are in common use for shogi and Chinese chess) through adapter programs such as Polyglot and UCI2WB.

It also contains supporting software for connecting with the popular Internet Chess Servers FICS and ICC for on-line play.

[8][11][12][13] Among its features is the ability of users to define and use their own custom variant chess pieces for use in games.

The Fairy-Max module is a chess engine only, but is packaged with XBoard, which serves as the graphical user interface.

[15] The author of the program has said "the goal of Fairy-Max is to make an entertaining but beatable opponent to play against in all kind of chess variants.