Kerbal Space Program’s modding community has four years of experience with the game, and it shows. Additions over that time range from bug fixes to physics tweaks to bundles of new modules that add entirely new building disciplines to the game. With the Kerbal Aircraft Expansion, KSP becomes a game about building and flying traditional prop-driven planes and helicopters. This hooks into the core game as much or as little as you’d like it to. Think you can give your prototype spaceplane a kickstart by ferrying it into the stratosphere on the back of a heavy cargo plane? Then go for it. You’ll need to learn how aircraft work first, however – and the game’s fundamental respect for the actual laws of real physics is held in high regard by the community.