Syncthing is not a Dropbox replacement, but it is an excellent file syncing system (more similar to BitTorrent Sync). I use it to sync my main source code directories and .emacs.d, and it does a tremendous job of that.
I'm looking at the practicalities of offering a hosted Syncthing service, as I've begun doing something like that just for my company. I think that if commodity Syncthing hosting becomes a reality, Syncthing is basically unbeatable.
it syncs directly between devices. a relay server is only used when the devices can't talk to each other (because thy are both behind a different NAT for example).
that's pretty much the definition of P2P, i'd say.
I'm looking at the practicalities of offering a hosted Syncthing service, as I've begun doing something like that just for my company. I think that if commodity Syncthing hosting becomes a reality, Syncthing is basically unbeatable.