XBoard is a free graphical user interface for the X Window System for chess programs such as GNU Chess and for the Internet Chess Servers. It also supports e-mail chess and playing saved games.
A port of XBoard to Microsoft Windows exists, called WinBoard.
Xboard/Winboard is also a popular GUI used by many free (most in the no-cost and a few-in-the-freedom sense) chess programs and a handful of commerical programs. As of 2003 there are in total at least 200 such chess programs.
The communication protocol that is used by chess programs to communicate with Xboard/Winboard can be found at http://www.tim-mann.org/xboard/engine-intf.html
Many other chess software both free and commercial support this communication protocol. Examples include Chessmaster, Chess Assistant, Chess Partner, Shane's chess information database and Arena.
Another alternate chess communication protocol is the Universal Chess Interface [?].
