A lot of web/mobile apps can store backups on your personal cloud storage ( Dropbox, Google drive, ... ). It's usually done by by creating a folder and storing the files that are needed for the app backup. Some examples I've seen:
Is there a standard for saving my app's backup folder on a user's personal cloud storage?
I imagine that if all developers use their own convention for this the user's cloud storage root will become messy if a lot of apps are used.