checkmate3 chess2 strategy2 3d board game1 ai1 ai opponent1 artificial-intelligence1 board game1 board-game1 brain training1 chess game1 classic board game1 cross-device1 difficulty levels1 game1 html51 html5 game1 javascript1 marble board1 minimax1 mobile portrait1 mobile-responsive1 offline game1 online multiplayer1 player vs computer1 private room1 puzzle1 single-player1 strategy game1 touch-friendly1