Starbound!
Site: http://playstarbound.com/
Community Forums: http://community.playstarbound.com/index.php
Server section of their forums: http://community.playstarbound.com/inde ... dding.102/
I was asked to put a server up for people in my community to play on, and to my surprise, this game has a TON of players right now:

This is at midnight on the east coast.
I have the server running on a linux server atm, it is a terraria looking game, the memory on the 64-bit linux server is about 250MB atm, but I can't really provide much more info than that right now.
The game is in beta, so I understand if you guys want to wait to provide this as a managed install until it is out of beta. Just thought I would bring this (seemingly large) game to your attention!
EDIT: I can see why it is in beta! The server is using around 30% of an i3-2130 ( http://ark.intel.com/products/53428/ ) with 2 players.