Topic: SDK For use with Rails
I've been FORCED to use IPB from Invision for several large content projects this last year. I can't tell you how happy I was to find out about PunBB in the last few weeks! Its tiny, fast, and works great along side Ruby on Rails. I posted up a Ruby on Rails plugin that provides wrapper models for all the PunBB data tables, as well as a login/logout generator that auto-logs you into the forums.
Grab it at svn://ahgsoftware.com/punbb_sdk/trunk
I hope this helps someone out, thanks for the great software guys!