The best open source alternative to Orbiter is Pioneer. If that doesn't work for you, our users have ranked more than 10 alternatives to Orbiter, but unfortunately only two of them is open source. If you can't find an alternative you can try to remove all filters.
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...
A game of missions, trade and space combat in the 31st century using the Pioneer Space Sim engine with many additions and improvements.
