Build rockets, space planes, space stations, rovers, landers, probes. Explore planets, moons, capture asteroids, set up a communications network, colonize a planet, mine for resources and much more. It can even simulate our solar system.

KSP at its core is a rocket building and launching sandbox. When creating a rocket you can place engines, fuel cells, structural elements, and even parachutes, allowing you to build a rocket in any shape and size. The end result can even look like a giant doughnut, which might be difficult to get it into outer space. Even if you fail, the entirety of the process is really enjoyable.

KSP is a shinning example of early release done right. The currently available game is fun to play, and the developers are constantly adding new content.

Kerbal Space Program puts into perspective how amazing the advancement of the human race is. It inspires you to learn our history, how we got here, and what we can do proceed.

The physics engine does a reasonably accurate job of replicating the fundamentals behind both orbital dynamics and rocket design, so by going through the tutorials and experimenting, you're actually learning some real rocket science.