Minesweeper.

Reveal every safe square to win. A number tells you how many mines touch that square, including diagonally. Your first move and its neighbouring squares are always safe.

Mouse: click to reveal, right-click to flag. Touch: choose Reveal or Flag above, then tap a square. Flags mark suspected mines; they do not prove a square is safe.

Keyboard: Tab into the board, use arrow keys to move, Enter or Space for the selected mode, and F to toggle a flag. Reveal an open number again to clear its neighbours when you have placed that many flags around it. Incorrect flags can still cost you the game.