Always nice that fan-community produces interesting sourcebooks. And sometimes I get to host them too. Our own Xathrodox86, with help of Hectorius, have produces three interesting documents. These are not based on any version or rules, just background information, with nice details.
Warhammer Fantasy Roleplay: Blood and Silver - A Tale of greed and misery v1.0
Military campaign set to the Border Princes, with long timeline and various other details.
Warhammer Fantasy Roleplay: Cultrum - Thin Red Line v1.0
Detailed background information about spy organization in the Empire.
Warhammer Fantasy Roleplay: Secrets of the Path - Disciples of the Serene King v1.0
Ancient Cathayn organization, with strange powers, powerful connections through the world, enemies and strange dark secrets.
You can also find these documents from my site Universal Rules and Timelines -page.