Made the mistake of watching a couple of lets plays of this that popped up in my youtube suggestions and I'm now addicted (30 odd hours in 3 days - yay gardening leave!)

Basically you get to build huge automated production facilities to strip mine an alien planet whilst protecting yourself from aliens who attack you when you pollute where they live. Although its alpha I haven't encountered any gamebreaking bugs yet - it certainly feels like the core of the game is there.

Thought I'd post it up for those of you that like sandboxy type stuff as its not on greenlight yet so might not have heard of it.