Minesweeper.

Reveal every safe square without hitting a mine. A number tells you how many mines touch that square, including diagonals. Empty spaces open automatically.

Mark suspected mines with a flag. On a phone, hold a square or choose Flag, then tap. Switch back to Reveal to keep clearing. On a computer, right-click to flag.

When a revealed number has the right number of flags beside it, tap it in Reveal mode to open its other neighbors. Incorrect flags can trigger a mine. You win by revealing all safe squares; flagging every mine is optional.

Keyboard: Arrow keys move around the board. Enter or Space uses the selected action. F flags a square. R reveals it. F2 starts a new game.