You might consider some sort of wiki software. MediaWiki (Wikipedia) and Confluence are two popular ones. They have the revision control and multiple editor support you're looking for. They can also be customized to add the bonus features you're looking for.

The downside is that you'll be administering a server and customizing it on an ad-hoc basis while you figure out how to organize the content and make it spit out the PDF format you're envisioning (that you might not be able to get perfect) and teaching everyone else how to use it properly. It might not even be appropriate if these procedures will be used once and then discarded.

The upside is that it's not Word.