The following new website is very impressive and is useful for playing Seirawan chess by correspondence: http://seirawanchess.appspot.com/

Tried it out. It's still very buggy.  Several times it wouldn't let me make a legal move.  But is a good start.  Hopefully they will continue developing it.

Gary,

"They" is me. It's a project I work on when I have time, but I hope to keep improving it. I fixed a bug this morning that was causing some moves to result in an error - it may have been what you were encountering. I welcome reports of specific problems; if I can track down the problems I will fix them.

Kevin Leuthold