This article is from the GNU Chess and XBoard FAQ, by Tim Mann email@example.com with numerous contributions by others.
I believe chess.net provides a Win32 command-line version of accuclock
that will work with WinBoard. Please see the documentation on the
chess.net server itself; don't ask the author of WinBoard.
I don't know whether chess.net provides versions of accuclock for Unix
at this time. Ask them.