I've written a simple forum in C# that is compatible with classic Amiga browsers.
It's got most of the basic features needed and is fully functional. It outputs pure html and should render properly on any browser.
I'm not sure if Cammy is still interested in doing this, so maybe someone else may find this to be a good starting point for their project.
Download the code here:
http://steve.odyfamily.com/downloads/raforums.zip