Gary Gygax's Cosmos Builder (2006)

Publisher Blurb:

Cosmos Builder provides fantasy cosmologists the tools to create a unique depiction of the realms above and below (and everything in between) that can be incorporated into any setting. While this book cannot include all possible options, it hits upon the most common elements of planes of existence and offers insight for deviating from and blending these elements to suit your needs, to craft new dimensions and the strange worlds that exist on them and where diverse dimension meet.

This book is a toolbox, filled with ready-to-assemble components that will allow you to quickly flesh out your vision of a cosmology. These tools are designed to let you to share your vision with others so they can adopt your cosmology (or portions thereof) to their campaign, regardless of which game system they use. The only thing they require is knowledge of how the tools in this book work, or an explanation from you about how your friends can use your cosmology with their preferred game systems.