Homebrew is a new vehicle building sandbox by Copy Bug Paste. The gist is you make a vehicle and drive it around to collect bolts so you can buy better parts to make better vehicles. It's not limited to buggies either. I've only been playing it for a few days so I don't have the parts yet to make more advanced vehicles like; hovercrafts, airplanes, hot air balloons, helicopters.
The developers have taken the ethos of Dream-Build-Enjoy. You get a very large map to scoot around in. There's also multiplayer and in the vehicle creator you can specify controls to different seats of your vehicle (for co-op).
"The easy to use building system is designed for the advanced, the lazy and the mingebags. It contains all the tools you'll need to bring your inventions to life and test them."
I haven't had this sort of giddy fun in a game for a long time. It immediately reminded me of Banjo Kazooie: Nutz & Boltz, but with an engineering degree. You can control gear ratio, suspension dampening, steering radius and so forth. It's an easy-to-pick-up hard-to-master vehicle editor. Check out the video preview / review I made. I'm probably going to turn this game into a video series as I document my attempts to make the most absurd vehicles I can think of.
Oh, and by the way, you can try a FREE demo!