MostAwesomeDude/bravo is a Minecraft server written in Python. Looking at what's happening around Minecraft, I think I should check it out. Especially after a bit of browsing - it seems to be a good mix of freeform building like Lego and (adjustable difficulty) monster-slaying gameplay. And since you can run your own server, which can now also be multiplayer, you can build your constructions together with others or share them (though they can also break everything if you let them). And it doesn't cost a monthly fee, which personally kept me away from Lego Universe (even though I bought the box).