While it may be b, and c. It surly is not, a; as you can find here: http://universesandbox.com/,
The free version is spectacular enough; however, the premium does a whole lot more. While it is $20.00 at the site, you can find it at http://store.steampowered.com/app/72200/ for ten buck-a-roos! This looks like a great educational tool, not only about our universe, but about gravity, (just a theory), as well."Universe Sandbox is an interactive space simulator for Windows based PCs. Unlike most astronomy software that just shows you what the sky looks like or where the planets are, Universe Sandbox is a powerful gravity simulator. You can add another star to our solar system and watch it rip the planets from their orbits. The free forever version allows you to explore and discover any simulation. Optionally you can upgrade to to the premium version for unlimited control, (http://universesandbox.com/about/)."
Sorry to sound like a sails-man.