Factorio is a game of factory management, in which you mine resources in an infinite 2D world, and then make an enormous automated factory to turn those resources into goods, and then turn those goods into other goods, and so on. This is made more complicated by the native inhabitants of the planet, who object to your noxious, belching industry, and so you also need to defend your stuff against the alien threat.
The game has been in development for a number of years now, and will be released on Steam on Thursday. However, the Steam release will also be seeing a slight increase in price, so if you're interested I suggest buying it now on the game's website for €15, as opposed to the $20 you'll have to pay after Thursday. There's also a demo on the website, if you just want to try it out.
I've been playing the game for over a year at this point, and it's really solid. Don't let the game's nominal "early access" status fool you! There is a great deal of content here, and it can easily consume hundreds if not thousands of hours, if it gets its hooks into you. (As it did for me! Shameless plug: I got so into it that I wrote my own calculator for the game, which I may revisit now that the Steam release seems likely to pull in a new wave of fresh players.)
There's cross-platform cooperative multiplayer, too! After the Steam release, maybe it would make sense to set up some sort of GWJ server? I've done a little bit of multiplayer, and it seems to work fairly well, as long as everyone has enough bandwidth to download the map when they connect.
The game also has good support for mods, and a healthy modding community. The vanilla game is quite solid, but there are some overhauls which significantly expand the game in a number of ways. There are also some more minor mods, like the Resource Spawning Overhaul (RSO), which changes the resource-generation algorithm in some interesting ways.
I highly recommend this game, in case that wasn't clear.