If you're bored or just have some free time, I recommend giving this "game" a try.
It's a really more of a simulator than a game at this point, thus the quotations, but there are planned expansions and objectives for future releases.
Right now, the only things you can really do are: build a spaceship, launch it, fly it around the planet or into orbit, or watch it crash and burn.
It has a real-world physics-simulator, so you can't just build anything and expect it to fly.
But building the ship is definitely the best part; launching and flying the thing stable is fun, but not so much when it spirals out of control and plummets to the ground (don't forget to add a parachute!).
Anyway, if you're remotely interested in spaceships, space, physics or engineering, definitely give it a try.
(Kerbal Space Program thanks to Victor)