Use mediawiki, the software that runs Wikipedia, to document. It doesn't easily go into book format, but hypertext is really powerful and easy to use. You can

Use mediawiki, the software that runs Wikipedia, to document. It doesn't easily go into book format, but hypertext is really powerful and easy to use. You can also embed powerpoints in it. Best of all, updates and versioning are easy as it's a living breathing hyperlinkable system with a full change history built in.