Ultima is a chess variant that is pretty popular. Its rules are here: www.chessvariants.com/other.dir/ultima.html. I think it would be good to add to the site.

Usually playstrategy leaves the fairy variants to pychess.

PyChess Variants can't add Ultima right now as it's not supported by Fairy-Stockfish. And while it's a chess variant, it's different enough that I think it could be on this site instead.

Thanks for the suggestion @PraseodymiumSpike
Whilst it looks interesting, we're unlikely to add Ultima Chess soon, as it has a few technical complications. I've made a note of the request however.

@PraseodymiumSpike Pretty popular? lol
It was pretty popular long ago. No one plays Ultima now. And this is very sad.