World-building isn't very easy. Coming up with an entire planet's worth of government structures, agricultural focuses, terrain layout, and on and on and on, can be tedious. Then you add in religions for all the regions and boy, that can really get confusing. Thankfully, there are those out there willing to do that work for you. The Beyond the Skies supplement for the world of Calidar is one such book. It's up on Kickstarter now.
The book is designed to be system-agnostic. That is to say, whatever gaming system you feel like playing, you can use this book for it. The book covers the various pantheons, the cults that brought the gods into existence, and the history of how those groups have operated in the world. But not just a book for DMs, there are special rules for players as well who show special piety for certain gods.
The campaign is about 1/3 funded with still 35 days left to go.