It has been probably half a year since I've last played Starforge and there was not much to do back then. You could shoot at some monsters and there was very basic building implemented. So how is it now?
Also, is Prison Architect that good? Like others said the price is a bit too high but then again I spent 25 Euros on the Arma 3 Alpha and the game turned out to be really good (if you find a decent multiplayer server that is; also the performance deteriorates after some time and it runs poorly no matter what graphics settings I use).
Kerbal Space program also looked interesting (at least judging by this article from Christopher Livingston on PCGamer, guess I gotta try the demo).