After being intronized Manager of Research & Development about two years ago, one of my first projects was to set up a set of technical documentation (in Microsoft Word format) to define rules to be followed by the .NET (and VBA) development team.
A documentation for CSharp rules, one other for ASP.NET applications, yet another for the rules database objects...
Now, although it is more and more complete, it is also more and more heavy and cumbersome, and finally less and less read (so followed) by the team, despite the code reviews and regular reminders.
Following a discussion with my brother (who is a talented developer much closer to open-source world than me), we talked about MediaWiki, which made me want to try to use it in order to centralize all our documents into a single repository easily reachable by all the team.
Article after article, link after link, we get quickly to the game. After only two weeks, much of our documentation is already migrated, a lot of new articles have quickly emerged, and this new tool is now interesting for everyone: the development team (and managers) can now quickly find the information they need to work properly, rules are now better followed.
As for the collaborative aspect, we currently limited editing to management, but we plan to allow each developer to contribute to the documentation with the establishment of moderation.