wetware: I agree that Compromise Chess is a should-be-here variant, but there are at least two possible checkmate rules and II am not sure which one is better. Although your ruleset makes perfect sense, the take-the-king variant also does, that is, if you have only one way to get out of check, you have lost the game. When you are not in check and have only one legal move, it should probably be counted as stalemate.

Move-and-a-half chess is an interesting idea, that I didn't hear about before. Probably only play-testing can tell whether games will not always be n times a single move, followed by a big series which leads to checkmate.

mangue : Yes, I would love to see multi-move variants here. They are well suited for turn-based play because the games are usually short. Marseillais is good, but my personal preference goes to Double-Move Chess (the take-the-king equivalent).