ProjectForum is a self-contained, easy to use but powerful wiki implementation.
It can be setup very quickly (no worrying about Web servers, CVS, hacking scripts, etc.),
and is optimized for workgroup collaboration.
Its probably the quickest and easiest way to get a full-featured wiki running on most any system.
Some of the features include:
support for multiple groups (i.e. wikis), and project areas within groups (sub-wikis)
forum-style posting as well as wiki editing
file attachments, images
complete version history
multiple authentication schemes
user activity tracking
branding support, choice of UI themes or create your own
RSS feeds available for forums, and include RSS in forums (group news aggregator)
build complex pages by including snippets from other pages or other web sites
The implementation is based on Tcl and Metakit, though these are hidden internally. Versions are currently available for Windows, Mac OS X, Linux and FreeBSD. There is also a hosting service (i.e. WikiFarm), and a demo server can be found at http://demo.projectforum.com.
The software is commercial, though there is also a free version (lacking only some of the more advanced features). More info and downloads at: