DokuWiki is a popular content management system based on wiki technology. It is built in PHP and distributed under the GNU General Public License.
How to create a website using MediaWiki
Mediawiki is the perfect solution for creating your own online encyclopedia, online magazine or blog. This software is quick, easy to install and completely free of charge.
Atlassian Confluence
Confluence combines powerful online document creation capabilities, tight integration with Microsoft Office to help people work better together, share information and build knowledge.