The Gravitron is a minigame in VVVVVV that is a wrapping room with two gravity lines on the top and the bottom. Spinning squares will come at you from both sides of the screen. The goal is to survive for 60 seconds, but you get a checkpoint at every five-second interval. The music that plays during this stage is Positive Force.
The Super Gravitron is an endless minigame similar to the original Gravitron. You can access it in the Secret Lab via a warp token in Vermilion's room. The goal of the Super Gravitron is to survive for as long as possible--since it's endless, you won't get any checkpoints. You can get trophies for surviving for certain times, with 5 seconds being the lowest and 1 minute being the highest. The squares in the Super Gravitron move at the same speed as those in the original Gravitron, but they have different patterns and they're usually closer together. The background and squares change color at an even pace, and the music played here is Potential for Anything, which is quite a motivating title if you think about it.