2048

Swipe to slide every tile at once. Equal numbers merge when they collide — join them all the way up. Arrow keys work too.

The trick nobody tells you is to pick a corner and never leave it. Keep your biggest tile pinned there, build a descending row alongside it, and only ever swipe in three directions — the fourth is what breaks a good board. Your score is not the tile you reach but every merge that got you there, so a tidy board that keeps moving beats a lucky one that stalls.