Incredibly detailed space combat simulation game. It's got voxels, multiplayer, heat simulation, kilometer long spaceships, real world materials, realistic asteroids, and awesome music.
Then things took a bit of a turn. Space cows, butter as a building material, living spaceships that heal themselves, and all manner of sci-fi concepts.
Want to build a granite mothership with dozens of fighters? You can do that.
A spinning battleship with a three meter thick titanium hull? Sure.
A butter asteroid-tug that melts whenever you turn on the engines? Of course!