Two players White and Black alternately put dominos into a square. The player who cannot fit a domino in loses, the other one wins.
You make your move by clicking into an empty square. Clicking the square again deletes this tentative move, clicking on a square adjacent to it confirms your move and completes the domino. The player who cannot move loses, the other one wins.
A rather different game is played with the same rules of moves, but with different payoffs. Again, White and Black alternately move. Each player that can move has to. The game ends when one player cannot move anymore. Then White gets for every empty corner field $1, and Black gets for every other empty field $1.