I really can't say enough good things about this game, but I will try to keep this as short as possible. Kerbal Space Program is a game/simulation about building rockets and exploring space. Each part you add to your craft is it's own independent physics object, so different ships will behave quite differently depending on how the mass of your ship is distributed or even experience a catastrophic failure if things are not balanced correctly. There are currently 6 planets to be explored and 9 moons. Their sizes range from a small moon of 13KM in equatorial radius to a giant (by Kerbal Standards) Earth sized planet with a equatorial radius of 6,000KM. Kerbal Space program is far from being a finished game however, and it is in constant development, as great as the game is now, it will only get better with planned features such as: A tycoon style campaign, a weather system complete with wind and turbulence, a re-entry heat system, more celestial bodies to visit including asteroids, and more things to do with your kerbalnauts outside of the space craft just to name a couple. And in addition to all of the things being done by the fantastic development team, the possibilities are endless when you add the fact that KSP has a robust modding community that is continuously turning out great new addons and plugins to make the KSP experience that much better. So check out the free trial version over at kerbalspaceprogram.com or pick up the full version for only a few bucks. Build modular space stations! Spoiler Build unmanned probes! Spoiler Send said unmanned probes to distant planets! Spoiler Did I mention build modular space stations?! Spoiler EDIT (I'm super excited about this update) Release Version .22 has been available to the public for a couple days now and I must say, I really like it- Career mode has made it's debut with the currency of "science points" which are earned through doing science and is used to purchase new tiers of a tech tree in the new R&D (research and development system). Though as a veteran player it's not as engaging for me- from what I understand it's meant for newer players to get a handle on the game so instead of starting with so many parts, they will begin with a handful of parts and progress from there and thus avoid being overwhelmed from the begging. BUT I am very happy with it, I'm playing around with it and using it sort of like an achievement system for myself, plus it's just fun to play this like a game with objectives than to impose the restrictions and objectives on myself.