celestia

Don't you wish you can just fly outside of Earth and into the universe? Explore the other planets and the nearby stars, and maybe even catch a glimpse of a comet or an asteroid? It might not be possible now to tour the Solar System or the universe (unless you are a billionaire!), but you can do this in the comforts of your home right in front of your computer. Celestia is an open-source space simulation software that lets you explore the universe in 3-dimension - stars, galaxies, planets, asteroids and a whole lot more! And the best part? It runs on Windows, Linux and Max OS X.