Extreme Planet Makeover [NASA]

If you ever wondered what kind of variables make a planet be like it is, then you'll love NASA's Extreme Planet Makeover. An educational tool that allows you to play with different variables and see how your own planet turns out.

You can fool around with planet size, its age, the type of star it orbits and the distance from it.

I can't help but remember one of the first BASIC programs I ever wrote, that plotted the kepler orbit of an object orbiting a "sun". Which, as a matter of fact, is something I wish this NASA Planet Makeover also showed up.