joshi tm: It's the name of a game invented in the early sixties. It's played on a regular Chess board. The King is the same and the object is to checkmate him or stalemate him to win the game. The other pieces are different. In regular Chess the pieces all move differently, but capture the same way, displacement. You know, occupying the square of the captured piece. In Ultima, all the pieces move the same way, but capture in different ways. I always used a regular Chess set to play Ultima, though I have thought of some different styled pieces that would be good to play Ultima with. There's seven different pieces as compared to regular Chess' six, so you need to mark one of the pieces. We did this by putting a bottle cap on one of the Rooks. You can also just turn a Rook upside down or put a rubber band around it.

http://www.chessvariants.com/other.dir/ultima.html
http://www.chessvariants.org/other.dir/ultimapieces.html
The first links has the rules and a breif history of the game. The second shows how the pieces move, though it uses the pictorial pieces instead of Chess pieces.