Free and low-cost enterprise wiki tools and open-source content management systems are plentiful. Covers the following:
- OpenSourceCMS
- Wikimatrix.org
- Drupal
- Plone
- Mambo
- Joomla
- WordPress
- PHP-Nuke
- XOOPS
- MediaWiki
- Wikispaces
- PBWiki
- DokuWiki
- TWiki
- Basecamp
Plone is at the high end with support for user defined content, workflows and versioning. WordPress is at the low-end. I am not sure whether I would really call Wikis content management systems, but I guess they do manage content. If you are interested in this area, you may also want to look at OSCOM which provides a list of both content management frameworks and content management systems.