I've been quietly working on the script behind the site http://medichan.org/
The only reason I wrote it originally was because the free host I switched to after having no reason to pay $120 for a year of Dreamhost doesn't support Perl or MySQL. It uses only flat files and runs fairly well. I have some improvements to make before releasing the source code, but what do you think? It's kind of a mix between a text board like kareha and a very simple web forum.
also bbcode is an amazingly dumb concept in the first place. if you're going to allow some sort of tag-based syntax just parse html and strip out unsafe tags.
A better concept is to parse HTML and only allow safe ones. Well, that's probably what you meant but it's better to be explicit about this stuff.