Universe Sandbox is a Windows-based simulator that lets you interact with the solar system and 1,000s of celestial objects. But Universe Sandbox takes this setup one step further, letting users run fictional (we hope) scenarios,
Smash planets together, introduce rogue stars, and build new worlds from spinning discs of debris. Fire a moon into a planet or destroy everything you’ve created with a super massive black hole.
Nice. It’s free to download and demo, and the suggested license cost for individual users is $25 (the author lets you set your own price, so you can go higher or lower than that).