TikiWiki is designed to be an international, clean and extensible Content Management System and Groupware that can be used to create all sorts of web applications, sites, portals, intranets and extranets. TikiWiki also works great as a web-based collaboration tool. TikiWiki has a lot of native options and sections that you can enable/disable as you need them.

Web Site: http://www.tikiwiki.org/