Tic-Tac-Toe — free browser game

Beat the computer to three marks in a row on a 3×3 board. You always play X first: click an empty cell to place your mark, then after a short think the computer places its O and the turn returns to you. Get three X's in a row horizontally, vertically, or diagonally to win; if the computer manages it with O first you lose. If all nine cells fill without three in a row the round is a draw. The scoreboard remembers wins, draws, and losses; press R or the restart button for a new round. Tip: when you have the first move grab the centre square — four winning lines pass through it. Before each move scan the board to see whether the opponent is one move from winning, and prioritise blocking that line if so.