This article is from the GNU Chess and XBoard FAQ, by Tim Mann firstname.lastname@example.org with numerous contributions by others.
XBoard is a graphical user interface for chess. It displays a chessboard
on the screen, accepts moves made with the mouse, and loads and saves
games in Portable Game Notation (PGN). XBoard is free software. It
serves as a front-end for many different chess services, including:
Chess engines that will run on your machine and play a game against you
or help you analyze, such as GNU Chess (topic [B.1] above) and Crafty
(topic [F.3] below).
Chess servers on the Internet, where you can connect to play chess with
people from all over the world, watch other users play, or just hang out
Correspondence chess played by electronic mail. The cmail program (topic
[D.6] below) automates the tasks of parsing email from your opponent,
playing his moves out on your board, and mailing your reply move after
you've chosen it.
The Web and your own saved games. You can use XBoard as a helper
application to view PGN games in your Web browser, or to load and save
your own PGN files.
XBoard runs under Unix or Unix-compatible systems. It requires the X
Window System, version X11R4 or later. There are also ports of XBoard to
Microsoft Win32 (that is, Windows NT or Windows 95) and to the Amiga.
See topics [D.2] and [D.3] respectively.