If you had a Java-capable browser, you could play Riley's Four Army Chess here. Move a member of each of your two armies each turn, if you can. You may move into check and capture members of the other friendly army.
Pawns move one or two orthogonally if the squares are empty, and capture one square diagonally.
You may move into check. There is no stalemate. Win by capturing both the enemy kings, or by moving one of your kings to the other's starting square, or starting a turn with the kings on adjoining squares.