Rails based Q&A WIKI type solution ?

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.