How to implement a cross browser uploader that supports a folder tree upload?

I need to implement a file uploader that supports drag and drop of files on a browser and it needs to support folder uploads (with sub folders/files).

Ideally it would all be done with html5 but only Chromium based browsers actually support the folder uploads. Also there doesn't seem to be any indication that Firefox / IE would be supporting this feature anytime soon.

These features would have to be supported in both Windows as well as Mac in (at least) the above mentioned browsers as well as Safari (on Mac).

Previously this was supported using Java but the idea is to move away from this as well as any Flash based solutions.

That said, what the sanest approach to achieve this technology wise? The criteria being: least amount of redundant code and least amount of hassle for the end user.