The File System Access API with Origin Private File System
webkit.org
webkit.org
This is sad... based on the title, I was hoping this will be a way for webapps to provide easily exportable data. But it looks like it's not going to like this, so webapps will be same closed black-boxes as before...
Really, what you're asking for is just more metadata about a file and some arbitrary organization around folders.
You know, something that was forever possible with every application which uses OS's file system.
There are still ways how this will not end in closed black-boxes.