Comment 2 for bug 451582

+1

I actually had looked for something like this (and still am, more or less) since 2006:
http://michaelshadle.com/2006/12/28/the-quest-for-the-end-all-backup-solution/

Duplicity came out the best choice except for Windows support :(

I don't see any reason it couldn't be made cross platform, all the tools are out there. I'd try to do it myself but I'm not that low-level...