Is there any UCI GUI for arbitrary variants?

Question

I have a UCI-compatible chess engine which I modified to play a chess variant (gravity chess, where all non-pawn pieces fall towards increasing rank). However, there's no easy way to play against the modified engine in a GUI, since it assumes the engine is playing either standard chess or one of a few variants. Is there any UCI GUI which supports arbitrary variants, or one that is easy to modify to support gravity chess?

Answer 1

CECP (xboard) goes quite far in allowing using the protocol to play chess variants, though I'm sure you can cook up something that goes beyond its limits.

FairyFishGUI is a minimal GUI that's used to have a simple GUI for new variants added to Fairy Stockfish, a variants chess engine. It should be fairly simple to modify to support your variant. The Fairy Stockfish project in general is a good place to start looking for how to support oddball variants.