Sky Nations is a multiplayer sandbox game where players can join together to build air ships(cannons and all!) and do battle across a vast world procedural world full of relics and machines from another age waiting to be plundered by daring sky captains and their motley crew.
As the game is in Alpha build, I do feel what is available is above and beyond what many other alpha builds offer. The developer is an extremely friendly and hard working fellow, always willing to offer help if you happen to be in a server with him.