Looks like the server component is not open source? It doesn't look like it would be hard to write an open source backend. I use Dropbox and a second copy back

Looks like the server component is not open source? It doesn't look like it would be hard to write an open source backend. I use Dropbox and a second copy backend up to my personal server (via Dropbox cli) for photos. Owning that data is too important for me to use a random service accessable only via a phone app.