XBoard (on GNU/Linux) and WinBoard (on Microsoft Windows) are free graphical user interface clients. Originally developed by Tim Mann, these programs are compatible with various chess engines that support the Chess Engine Communication Protocol such as GNU Chess. It also supports Internet Chess Servers, e-mail chess, and the playing of saved games.
Recently WinBoard / XBoard has been enhanced a great deal, and the Chess Engine Communication Protocol was extended to meet the needs of modern engines (which have features such as hash tables, multi-processing and end-game tables, which could not be controlled through the old protocol).
XBoard has always been supportive of Chess variants, such as Suicide Chess or Crazyhouse, acting as a client for Internet Chess Servers that offered such variants. This support has now been extended to all of the World's major Chess variants: xiangqi (Chinese Chess), shogi (Japanese Chess), makruk (Thai Chess) and many Western variants on boards of deviating sizes (e.g. Capablanca Chess). It offers a Westernized representation for these games, but the almost limitless configurability of WinBoard does allow a high-quality traditional oriental representation of these games.
Another computer chess protocol is the Universal Chess Interface (UCI).