Celestia is a simulation of the entire universe, based on currently known astronomical information.
It includes beautifully rendered planets, moons, and some smaller orbital bodies such as Mir and the International Space Station. Celestia is not limited to our solar system; you can visit other stars, or even travel outside the galaxy.
You will find models of extra-solar planets in orbit around those stars for which we have evidence of planetary bodies.
You have complete control over time and space, so you can view the stars from your chosen location and epoch. In addition, it is possible to create scripted presentations for complex demonstrations.
It is an open source application. You can get the source code and applications from here