From Humble Monthly.

SimpleRockets 2 is a fully 3D space sim that lets you build rockets, airplanes, rovers, or anything you can imagine and explore highly detailed 3D planets. Sharing is a core concept in SR2 and it has built-in capability to easily share crafts and saved games with the community. With SimpleRockets 2, it is easy to get started, but advanced players can dig into technical details if they are interested in the math behind rocket engines and orbital mechanics. Included are 17 different challenges to put your creations to the test. This is actual rocket science! Join us as we enter Early Access and continue adding new features, such as the Planet Builder and Campaign Mode.