Samba, rsync, sshfs, even fusefs... but there's seemingly nothing that can keep your files yours across your own devices without extensive hacking/setup, suspicious EULAs, MitMs, etc. We can build it, but normies can't

Works so great on new devices like smartphones. Except not.

And so easy to set up on a home computer. Except it's not always on and doesn't come with backups.

I'm not saying S3 is where it's at but might need a bit more than just Samba. Or maybe you don't but people who need Dropbox do.