Kerbal Space Program (PC) Steam Key Global

This is a very well sandbox game. Also with something like a store. The physics and the mechanics are good. If you have not enough you can easily install mods to have more fun. I withdraw 1 star, because of the DLC, wich is not so good. And you can have better content with mods.

The game is incredibly complex but rewards you for doing things right. It will take many hours to even get your spacecraft to do ANYTHING but it will be very satisfying once you make it to the moon or otherwise anything else you wanted to do. 5 stars

Actually, the best game about explorating space. A little bit complicates if you don't know the space specific languages, but you will learn easily :)

The best game that ever happened to me.