I have found Wikis to be a really useful tool for documentation in any environment.
For Wikipedia it has been such a success because it allows editors to collaborate in an article without having a direct approval of any modification but doing any rollback if the change was incorrect.
For corporate environment a wiki is a clear winner. I have seen most people just do a document that it is left to be rotten as people share it over email and is gradually outdated. Just having a URL with a wiki page is a much more useful resource to keep any documentation up to date.
My preferred Wiki software is MediaWiki because it is extremely intuitive and fast, has a clear UI design and is actively developed (compared to other wikis like MoinMoin or XWiki that have no clear UI or are just bloated). MediaWiki is being used at Java projects like Eclipse, even being written in PHP.