Twiki is another implementation of the wikiwikiweb concept, written in Perl. The Twiki wiki is at http://twiki.org/ and the Twiki development site is at http://sourceforge.net/projects/twiki/
Twiki has been designed to be useful in a corporate environment and for this reason it can be configured to far more restrictive in what it permits non-authenticated users to do. It can be installed under Apache on unix and also under Windows.