enough to be used in as wide a variety of situations as possible. There's a choice of backends (currently MySQL, Postgres and SQLite, but people have expressed interest in writing a flat-file backend too), and since it's a toolkit - providing methods - rather than an actual application, you can use it wherever you like.
OpenGuides (also available on CPAN) is built on top of CGI::Wiki. It's a complete web application providing a management system for a collaboratively-written city guide. The London install is currently the largest - see http://openguides.org/london/ Other installs are linked from http://openguides.org/
OpenGuides uses CSS and the Template Toolkit and our aim has always been to produce something completely suited to its purpose, rather than shoehorning our content into something that looks and smells like every other wiki site out there. It does RDF too, so it's all semantic and stuff.
Both CGI::Wiki and OpenGuides are in active development. They're certainly not what I would call mature yet, but they're definitely usable. Here are the links for the dev lists: http://www.earth.li/cgi-bin/mailman/listinfo/cgi-wiki-dev http://realprogrammers.com/mm/listinfo/openguides-dev
And the code is on CPAN: http://search.cpan.org/author/KAKE/
Kake