Options for Online Collaborator Authoring?
 

Hey gang
I am writing a non-fiction book and my co-author lives in New York and I live in Virginia. So, I am looking for some kind of app/software, hopefully online with offline abilities, that will enable me and her to collaborate together on the book, but yet also keep our own original versions/drafts.
I guess something like Windows Cloud or maybe Writeboard
http://writeboard.com/

I also know of Zoho Docs, which seems like Google Docs.
But, I wonder about the security of online document software?

Really, I have not found something like I want; a dual online/offline app that can store local and online versions of our separate drafts with time-stamped back-ups. Additionally, I would like something where her and my drafts are somehow read-only. For example, while I could edit my own drafts I would only be able to read her's, but not edit them, and vice-versa.

I don't know of any such software and have no experience with Google or Zoho docs and so I wanted the opinions of my friends in the linux community on what software might be closest to what I need.
Additionally, I am using Linux exclusively, and she uses Windows exclusively.
Thanks for any ideas/help

You could give Zimbra a try.