XBoard and WinBoard are graphical user interfaces for chess. They display a chessboard on the screen, accept moves made with the mouse, and load and save games in Portable Game Notation (PGN). They serve as front-ends 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, Crafty, or many others. A list of compatible engines is available.
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 and chat. A list of compatible servers is available.
Correspondence chess played by electronic mail. The CMail program (which works with XBoard only) 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.
PGN viewer. You can use XBoard or WinBoard as a viewer and creator for game files recorded in PGN (standard chess notation).
XBoard runs on Unix systems, while WinBoard runs on 32-bit Windows systems, including Windows 95, 98, NT, 2000, 2003, ME, and XP. Tim Mann is the primary author of both, though there have been many other contributors.