The Ysgarth System
Book 3 - Worldcraft
From the introduction:
[This] third book goes into detail on background design and applications of the rules in the society of the world of Ysgarth from which the game takes its name.
Using the Ysgarth campaign setting; additional setting details for Ysgarth, Isgartt, and Uttgart.
A little know RPG gets the once over.