Knowledgebase and Hidden Features... Some of them are even not hidden...
This section will be kept short, so you can take a quick view this and then for updates.
There is a Git repo with custom extensions for RR.
E.g. the Blender Connection.
The git location is: https://github.com/BinaryAlchemy/RoyalRender-OpenExtensions
You are free to add any of your extensions.