2048
Slide all the tiles at once. When two tiles with the same number touch, they merge into one with double the value. Build a 2048 tile, then keep going as far as you can.
← ↑ → ↓ or WASD slide the tiles; on a touch screen, swipe the board. U or Ctrl+Z undoes a move. Your game is saved in this browser, so you can come back to it.