Chain of Worlds
"What we should do at some point is just make a setting, take a party of adventurers, drop them in there and say 'Go Wild.' No metaplot."
The Chain of Worlds is a series of polyhedral islands scattered in the Astral Sea, on average about the size of a kingdom. Some islands are linked by elemental veins, such as rivers through the Astral Sea, others are isolated by more dangerous elemental manifestations. The magitech to travel the open Sea between worlds is fairly common.