Lifehacker have a great how-to showing how to install MediaWiki (The software that runs Wikipedia) on a local PC using a piece of software called WAMP.  WAMP is a useful tool that installs Apache, PHP and MySQL like PHPTriad used to do in the past.

The wiki could be useful for any number of things, IT infrastructure documentation, Procedures in a workplace, Best Practices for writing a blog, writing styles etc.  Oh, or maybe some kind of a giant encyclopedia

http://www.lifehacker.com/software/wikipedia/geek-to-live–set-up-your-personal-wikipedia-163707.php