This article is from the GNU Chess and XBoard FAQ, by Tim Mann firstname.lastname@example.org with numerous contributions by others.
The only way for two humans on different machines to play chess in real
time using XBoard is to use an Internet Chess Server as an intermediary.
That is, each player runs his own copy of XBoard, both of them log into
an ICS, and they play a game there. Two copies of XBoard cannot
communicate with each other directly.
Instructions on how to get started with Internet chess are included with
the XBoard distribution. The network addresses included in the XBoard
distribution may not always be current. The oldest and largest ICS is
the Internet Chess Club at chessclub.com, which now has a fee for
registered use, but still allows free unregistered use. There are also
many newer sites with no fees, using the Free Internet Chess Server
implementation (FICS). Some current FICS sites are freechess.org (the
most active) and eics.daimi.aau.dk. On all these machines, the port
number to use is 5000.
Note: If you don't have network connectivity to any ICS site, you can
run your own server using the FICS code. You can get a copy by anonymous
ftp from the Internet Chess Library (topic [A.3] ). The code is changing
rapidly, so send mail to email@example.com and/or log into the FICS
server at freechess.org and ask the administrators there for current
The cmail program included with XBoard lets you play email postal games
with another human; see topic [D.6] .
Two humans can play chess on the same machine using one copy of XBoard
in Edit Game mode, but the clocks don't run in this mode, so it's of
See also topic [F.2] , Winsock Chess.