minesweeper
A little classic. Find the empty squares, flag the mines, and try not to click the wrong one.
Your first square is safe.
Click to reveal. Right-click to flag. On a revealed number, click again to open its neighbors when enough flags are placed.
On touch screens, turn on flag mode. With a keyboard, use the arrow keys, Enter to reveal, and F to flag. Click the smiley to start again.