One button, four levels, no checkpoints. Hold to jump; hold again in mid-air to catch a yellow orb. Portals flip gravity or turn you into a ship you steer by holding. Touch anything sharp and the run starts again from the beginning — that is the whole game.
Space, W, ↑, click or tap to jump — hold it down to keep jumping. In a ship, hold to climb and let go to fall. Esc goes back to the level list.