From publisher's website:
Chaos Worlds are individual Dungeon World setting books, written by Brendan Conway and illustrated by Juan Ochoa. Each book comes with its own setting, compendium classes, artifacts, monsters, fronts, and rules changes to help you take Dungeon World into strange and interesting new fantasy settings.
All the Chaos Worlds use the Dungeon World system. You can read more about the system, and you can even find the free SRD online. Dungeon World is Powered by the Apocalypse. It uses a simple system: you roll 2d6 and add a stat. On a 10+, you’ll get a full success. On a 7-9, you’ll get a success, but with some cost or complications attached. On a 6 or less, the GM gets to say how things go wrong.