Anti-Gravity is a physics-based puzzle-platformer level for Half-Life 2: Episode Two.
Dr. Kleiner has asked Gordon Freeman to help him with an experiment involving his latest invention, the Anti-Gravity Cube. This cube has the power to ignore motion and gravitational force. Kleiner wants Gordon to put it through a stress test by using it to overcome a series of platforming obstacles. The player has the Super Gravity Gun, the only device strong enough to move the cube. The testing facility the player is in has low gravity, which helps facilitate the platforming obstacles the player must face.
Half-Life 2: Episode Two