Fourth World is a drift of the Dungeon World rules to play in the setting of Earthdawn. It’s built for longer term campaigns, and is a bit more crunchy than straight Dungeon World (but nowhere near as crunchy as Earthdawn).
The current version is 1.4, and it has drifted further from RAW Dungeon World. Version 1.5 approaches completion, and will drift even further (to the point that this will be the final 1.x version).
If you have questions, requests, or comments, you have a couple of weeks to voice them and influence version 1.5, so fire away.
(A link that leads to all the posts tagged with Fourth World on my blog, which includes all past versions and some mechanical analysis.)