If you are willing to trust your privacy to strong crypto (something you probably would want to use even on a private network), ObjectiveFS (https://objectivefs.com) might be worth looking into.
Being able to work on a totally disconnected network is different. Maybe if you could support Eucalyptus's S3 or another backing store like that it would be equivalent (and that might be interesting).
I'm sure plenty of people are fine with an Internet-connected, AWS S3 backed system, though, especially with additional crypto.