The free MediaWiki software is best known for powering Wikipedia, but you don't have to be writing an encyclopedia to put it to good use. Extend, skin, and customize MediaWiki to create any kind of easy-to-update, collaborative web site.
When and Why MediaWiki?
MediaWiki is arguably the most advanced, install-it-yourself, free wiki package available. A wiki is an editable web site; you can change each page's content without having to log into a content management system like WordPress or access the server via FTP or other means—you just hit the edit button. While MediaWiki is built for public web sites that anyone can update, like Wikipedia, you can customize it to limit access to certain users. Like WordPress and Firefox, MediaWiki is extendable via plug-ins that add functionality. MediaWiki is also skinnable, which means your wiki can sport a custom theme so it doesn't look just like Wikipedia.
MediaWiki's greatest strengths are that it makes web site pages extremely easy to update, and it makes managing page changes by multiple users very easy as well. S