9. Four-player chess variants
These chess variants are for not two, but four players, playing in two teams: Yellow and Red play against Green and Blue. The teammates support each other, and attack the other team together.
The game ends when someone gets checkmated. Then the checkmater team wins and the other team loses.
More detailed rules: Four-player chess. These variants differ only in the board and the movement of the pieces. The general rules are the same.