> Are you going to use a third party application for backups?
macOS, Windows 10, and Ubuntu Desktop all come with built-in, incremental backup solutions that work well (at least for me), so I think that need is taken care of.
There are a number of apps on iOS and Android that allow arbitrary folders to be synchronized with a server or NAS. I'm using Resilio Sync, and it seems to work.
> How about sharing?
I've written a design doc for sharing that I'm about to build out. I'll share it with you.
> The application you are building looks interesting!