Universe Sandbox is a sandbox based game where you can create (or destroy!) a huge array of celestial objects. You can do nearly anything, add rings to the Moon, collide galaxies, turn the sun into a black hole and much more. The game is free, but you only have limited options after an hour of gameplay.

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Official website: http://universesandbox.com/

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Videos






Yeah, I'm a big fan of astronomy and physics in general so I'm hooked on going random stuff in this game. Pretty cool.