Kerbal Space Program

A great resource I like to share:

It is a very realistic game using real physics.

Kerbal Space Program (commonly abbreviated to KSP) is a space flight simulator developed by Squad currently in public beta development for release on Windows, Mac OS X , and Linux. The first public version was released on June 24, 2011, and is currently sold on the online official KSP Store, and since March 20, 2013, through Steam's early access program,where it reached the top 3 best sold games.[4] Updates have been continuously released. KSP has large support for game mods and a large community to create them,[5] which developed shortly after the game's initial release. Notable members of the space industry have taken an interest in the game, such as NASA.

Official Link:

https://kerbalspaceprogram.com/