The beast is the last of those that I know of, and I am sure that this is the one you are referring to.
The rest is rather a side note, but when I first got on the rails, I asked similar questions, aka, what is the best blog, cms, forum, etc. use? As it turns out, the Rails community is generally interested in use cases that aren’t suitable for plug-n-play web applications, so most people end up folding their own to fit their needs, exactly if they find it possible to build such an application in Rails . The good news is that I think I remember that this beast looks like 800 lines of code, so it may not be too burdensome to upgrade from 2.2ish rails or just copy the logic needed for your forum.