Kerbal Space Program Standard Edition

Kerbal Space Program is a spaceflight simulator that teaches orbital mechanics by letting you get them wrong. You design rockets part by part in the Vehicle Assembly Building, launch them, and find out whether the staging, thrust-to-weight ratio and centre of mass were what you thought they were.

The physics are simplified but honest: orbits are real orbits, transfers need planning windows, and aerodynamics punish a badly shaped fairing. Career mode adds contracts, a budget, a tech tree and an upgradeable space centre, while Science mode strips out the money and Sandbox gives you every part from the start. The crews are Kerbals, small green astronauts with an unshakeable enthusiasm for missions that are not going to work. There is no official multiplayer — co-op exists only through community mods. The Making History and Breaking Ground expansions add a mission builder with historical missions and robotic parts respectively.

The Standard Edition is the base game with neither expansion. Keys activate on Steam or GOG. One Steam variant is region-restricted, so check the region before buying.