n01getsout

MediaWiki is the software that powers Wikipedia. A Wiki is a set of pages on a website where any reader can freely modify the content of the page or even add new pages. You can require that users register to get permission to change the wiki. Media Wiki keeps a history of all changes to a page to allow you to easily restore a page to an earlier state. For another great example of how MediaWiki can be used for different sites, take a look at what F-Spot has done with it.