I am investigating how to build a site similar to www.faqfarm.com which is a Q&A wiki. They use mediawiki, which is very popular PHP based that wikipedia uses. I suspect they had to highly customize the code and that taking a Rails based wiki would be easier to customize, although the feature set that these come with might be less. The two that I saw saw instiki and hiki, and some other piki type things that seemed only small personal type wikis.
Any advice or info would be appreciated.