I've grown rather fond of a game that still has beta status, early access on Steam.
It is a bit like minecraft but it's more about building working machines. Right now, there is only the creative mode available where you can actually have all blocks and parts in abundance and just fumble around building stuff. It's very basic mechanics, so don't expect to have studied in order to play this. The first driveable vehicle can be buildt in less than 5 minutes were most of the time is used for understanding how to build things.
YouTube is full of videos were people show off their creations or set themselves challenges to master when they play in one world, meaning multiplayer. It's no MMO! You open a world and invite people. There might be public worlds later on but right now, not that I know of them.
There will also be a survival mode later, were you actually have to somehow craft or find the parts you use for building and there will be farmbots that will mean to harm you. (I guess "killing" those bots will let you loot parts but that's just a theory from me.)
So, click over to YouTube, type "scrap mechanic" into the search bar and enjoy.
I certainly do!