Every turn you make two moves in a row.
How to play
Each turn a player makes two moves in a row (White's very first turn is a single move to keep things fair). The two moves may use the same piece or different ones. You may never leave your own king in check, and a first move that gives check ends your turn at once, so the opponent always gets a chance to escape. Checkmate wins; no legal moves while not in check is a stalemate (draw). Pawns promote to queens; no castling and no en passant.