software - Tools for science-based world building?

I tend to lean towards science-fiction and fantasy, so world building matters a lot to me. A while ago, there was a question which asked how to go about organizing your universe, which was interesting, but what I would like to know is: are there tools available that help with the world-building process itself?

I don't just mean from the perspective of just suggesting ideas, but rather would like something from a more science-based perspective. Ideally, I would be looking for a tool that could take data like circumference, moons, distance from the sun, tilt, and so on,and then be able to get data back like gravity, day/night/season/year etc. cycles, the planet's climate, and so on.

If it helps organise that information as well, that would be a bonus, but I don't mind a single, stand-alone tool that focuses specifically on what I'm looking for.

Edit: I've been digging around a bit on Google to see what I could find, and have come across an interesting piece of software called Fractal Terrains from ProFantasy that allows you to randomly generate a world. I've played around with the demo version a little, and you can change things like tilt, average rainfall, greenhouse, and a few other variables, as well as get different maps showing climate, altitude etc., but it doesn't seem to take into account its relationship with any nearby suns, or moons etc., or work out the seasons/cycles.

Still, it's pretty close, and it seems that it can partner with another piece of software they've developed called Campaign Cartographer, which makes the whole package pretty interesting.

However, if anyone else has got something similar to recommend, that would be brilliant.

Answer

SimEarth might work well for you. As I remember, in addition to the Earth simulation, there was Martian terraforming as well. It is an old DOS game; I wish Maxis had updated it for modern computers.

Something that might also be interesting is EdGCM, the only global climate model I know of that will run on a PC. Changing the forcings in model can provide some interesting effects - global cooling, global warming and so on. For science fiction scenarios set in the distant past, (try the Iceball Earth scenario) an alternate present, or set in the future, it should provide some climate related ideas.

Although they are not software, older RPGs like Traveller and Space Opera included systems for generating solar systems and planets.

For terrain, try VistaPro. Also an older program, it works quickly and can use real-world DEM data (sections of the Earth and Mars are included) or randomly generate landscapes. Try using something like part of the southern US and raise the sea level a hundred feet or so for an interesting effect.