The Great Elemental Netbook: A Guide to the Inner Planes, Part 1

From the introduction:

The Great Elemental Netbook is intended as a supplement to [adventuring in the Inner Planes]. It gives information about the inner planes, and about things connected to them.

User summary:

The Great Elemental Netbook was distributed in two parts only to manage the size of the document. The material is organized topically, and the division occurs at a logical place; however, the materials are intended to be used together. The book makes frequent reference to The Inner Planes and in many ways is a major expansion to the official product.