The best Exploration Game alternative to Celestia is Pioneer, which is both free and Open Source. If that doesn't work for you, our users have ranked more than 25 alternatives to Celestia, but unfortunately only two of them are Exploration Games.
Pioneer is a space adventure game set in the Milky Way galaxy at the turn of the 31st century. The game is open-ended, and you are free to explore the millions of star systems in the game. You can land on planets, slingshot past gas giants, and burn yourself to a crisp flying...
In this app you can explore almost any moon or planet of our solar system and visit remarkable nearby stars and see their location in the Milky Way. But you can also change existing bodies or add new ones and make a solar system of your own.
