I shall, somewhere in the next two or three lines, write the words "multiplayer survival sandbox with building and crafting" and I don't want you to see those then skim the rest. Pay attention, okay? Scrap Mechanic will be a multiplayer survival sandbox with building and crafting but wait wait wait you can build vehicles and machines like rocketcars and buggies with impractical numbers of wheels and suspended monorails and VTOL flying machines and walkers and devices that seem to flail wildly with no real purpose until they destroy themselves. See, that was worth sticking around for, wasn't it? With a little more patience, you can see all those in a trailer too.
You (yes, you!) have crash-landed on an automated agricultural planet whose robots have forgotten they're supposed to harvest crops and not human skin, muscle, bones, teeth, marrow, hair, eyes, and humours. I assume that's why they're trying to get ahold of you, anyway. So off you go, scavenging for parts to build shelters and all manner of machines that go go up tiddly up up and down tiddly down down. I do particularly enjoy how some of the vehicles unfold as they power up.
Multiplayer survival is the big goal, with bots and players all baying for your teeth, marrow, hair, eyes etc., but Scrap Mechanic at this stage of development is only a single-player 'creative mode' sandbox. Developers Axolotl Games are looking at going the early access route, and are having a crack at Steam Greenlight too.
Axolotl say they started on this after making a Xbox 360 test port of Minecraft. I am glad they decided to do more than change the name. Or add zombies.