Free and low-cost enterprise wiki tools and open-source content management systems are plentiful. Covers the following:
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.