DokuWiki is a simple to use Wiki aimed at a small companies documentation needs. It works on plain texts files and thus needs no database. It has a simple but powerful Syntax which makes sure the datafiles remain readable outside the Wiki.
When I worked at a law firm here in Vegas, ailment it seemed like we were continually getting “Procedure Documents” on how things are supposed to be done. A wiki like this would have been perfect for keeping procedures updated.