Kerbal Space Program

Kerbal Space Program is a game about a green humanoid species, named Kerbals, starting a space program. Superficially similar to Orbiter, the difference between the two has been likened to the difference between making to-scale miniatures for architectural design and playing with LEGOs with rocket fuel in them. In its current state the game is little more than a sandbox. You're set loose upon a space center complete with a vehicle assembly building and a launch pad, a bin full of rocket parts, ground personnel composed entirely of yes-men who build and wheel onto the launch pad anything you design no matter how crazy it is, and some astronauts to crew your creations. There are only a handful of parts, but the community is already cranking out fanmade addons at an impressive pace.

Its official website and download location is here, and a trailer for the game can be found here.

This game contains examples of the following:

Little Green Men: the kerbals are this
Cloudcuckoolander: Jebediah Kerman, who always smiles all the time, no matter what is happening. Unless something goes wrong.
Colbert Bump: Sips of the Yogscast posted a video about KSP. Minutes later, the server hosting KSP's website and forums imploded.
Oh Crap: Bill & Bob Kerman always look worried whenever the spacecraft is doing anything other than holding still. All characters do this if something explodes. If Jebediah ever stops grinning... see above.
- Bob will always look terrified. He'll only calm down if the craft is confirmably drifting back to the surface slowly via parachute or has come to a complete, safe stop.
Obvious Beta: Well yes, but it says right on the main page that the game is still in development and is in little more than a prototype-ish stage.
Sci-Fi Writers Have No Sense of Scale: The developers avert this but the use of this trope in media has caused some confusion among players less familiar with actual astronomical scales. Even among those familiar with space fight don't always remember exactly how big space really is. For instance, some have suggested ignoring time acceleration (ie being able to increase the speed of the game) and instead allow the program to run essentially in the background to allow for realistic flight during extended missions. Even acknowledging that a single mission would very well be months long, they don't seem to realize that most of that time would be spent doing... nothing.
- The distances are less than they would actually be, but that's due to the Space Compression. The scales for Kerbin/Mun/sun are roughly the same as for Earth/Moon/Sun accounting for it.
Self-Imposed Challenge: Making ridiculous rockets, making manned ballistic missiles, making space shuttle equivalents, spacecraft that look like specific patterns, achieving orbit, reaching relativistic speeds, getting a huge and completely pointless concrete cube into orbit, landing on the sun, landing on the moon, landing on the other tiny moon (latest beta version), etc.
Snowy Screen of Death: The individual video feeds for each Kerbal will cut to static if they are killed.
Space Compression: To cut down orbit times and prevent the game from becoming astronomically boring, the planet is a mere 1200km in diameter.
Space Is Noisy: Even in the depths of space, you can still hear rockets and explosions.
- Partially justified in that most of those explosions happen either in-atmosphere or when you're still attached to the thing blowing up/making noise, giving the sound a medium on which to propagate to your ears.
Stuff Blowing Up: Rocket fuel is an explosive after all.
Video Game Caring Potential: Some players equip their crew capsules with parachutes and try to land them as close to the Kerbal Space Center as possible...
Video Game Cruelty Potential: ...while others take gleeful pleasure in sending the hapless trio to die in the cold blackness of outer space. Or just blowing them up.
Wide Open Sandbox: In the current version of the game, money has no importance and there are no goals.