From the introduction:
Welcome to Sights Below the Moonsea, a brief guide to the Zethlentyn Protectorate and its history, inhabitants, and traditions. This guide is far from exhaustive. It is a living document that receives updates as more areas within the Protectorate are explored and developed. The guide serves two purposes.
Firstly, it provides background that could be useful for dungeon masters who are running the Swords and Spies Below the Moonsea series of adventures as well as the future adventures set in the area. The guide is not required to run the adventures, but can provide extra information for games with curious players who wish to delve deeper into the background.
Secondly, the guide serves as a common base for anyone wishing to set adventures in the area. A hidden chapter (available by request) has additional information on some of the long term plans for the setting and some of the hidden machinations happening behind the scenes.