Kerbal Space Program 0.25 (OS X)

Kerbal Space Program is a multi-genre game where the player can create their own space program. In the game, you must build a space-worthy craft, capable of flying it's crew out into space, without killing them. At your disposal is a collection of parts, which must be assembled to create a functional ship. Each part has it's own function and will affect the way a ship flies (or doesn't). So strap yourself in, and get ready to try some Rocket Science!