Making the rounds today is a fun little physics game, Super Planet Crash. On its face, it’s simple: start with an Earth-like planet in a random stable orbit around a star, then add additional orbiting bodies (up to 12 max) with masses ranging from the mass of Earth (1X) to a dwarf star (30,000X Earth mass) and watch as all those gravity fields interact. The hard part is depositing your planets in such a way that they orbit for 500 years without ever going more than 2 A.U. (twice the diameter of Earth’s orbit around the Sun) from the primary. You get bonuses for planets in the habitable zone and for “crowded” arrangements.
I managed to get the #85 top score with this scenario (dwarf star in tight orbit with primary, 11 Earth-like planets in the habitable zone).