Where I can find an engine like OFPS Open Feedback Publishing

I'd like to write a little book on personal topics together with two friends of mine, remotely located. Do you know of any FOSS content publishing system like the one from O'Reilly (OPFS)?

I saw the one that powers the django book but It seems that the code It's not released yet. I accept any kind of backend technology for this project.

I'd like to:

edit the book on the web and let my friend do the same after authentication.
anyone of us could comment other's entries.

Solution

OK, I'm going to roll out my own solution following the direction written here. I like a lot thigs like bitesizeedits or leanpub. The base will be a multiuser platform: mu. I'm quite fond with wordpress and as version control I'm happy with GIT. The commenting system will be digress.it.