Obviously wroteStarbound. It's like a 2D Minecraft, but you can travel from planet to planet..and you have some missions sometimes (they help you progress). It's procedurally generated.
Very random game. I've been mostly playing it online with friends. And in singleplayer mode, each one of my friends had different things happen to him. One has met a lab full of brainwashed monkey that were attacking him, another one found a friendly community that he could trade with etc.
It's still in Beta, but doesn't feel like it. (other than it taking a lot of time to open sometimes).
Did you encounter any issue while connecting to your friend's servers ? I tried everything from Port Forwarding to Hamachi but it never worked for me !
Had to stick to singleplayer mode. Still, this game is a lot of fun, and I highly recommend it to anyone who like the genre.