Game Courier supports many different games. Here is one picked at random:
Naydorian Chess - an hexagonal variant from the fictional realm of Shadowgard

Russian Fortress Chess

If you had a Java-capable browser, you could play Russian Fortress Chess here.
Keys "s"=save "l"=load "b"=back once

Indigo and Azure are the Blue team. Maroon and Scarlet are the Red team.

You may capture a unit from an allied army, but you do not check the allied king. You may not move into check. If a king is checkmated when his turn comes around, his whole army vanishes. If there is no legal move, skip the turn. For this reason, stalemate is unlikely, so all pawns promote to queens.

In negotiating the barriers, knights are assumed to move first orthogonally. I couldn't figure out how to handle the en passant rule, so I skipped it. I may add the option to arrange the pieces in your fortress as you like at the onset.

I figured the pawns could capture around the corner of the fortress, but that bishops could not sneak out the rim of the door.

Thanks to Bishop Fish and Veronica Reid for help with the debugging.

Russian Fortress Chess

Hans Bodlaender's Chess Variants
Hans Bodlaender's Chess Applet

Ed's Chess Variants