BitTorent Sync is a great tool for startups.
blog.vrypan.net
blog.vrypan.net
So which is it? Immediately or fast? How would the transfer rates to a remote sync compare with a NAS replication stream? How would the LAN file synchronisation compare to local NAS?
I guess that a cheap NAS would probably perform the same or maybe worst. I don't know about a high-end NAS on a very fast and fine tuned switched network, but that's usually outside the scope of most startups in their early stages.
Also there's an iOS and Android version:
https://itunes.apple.com/us/app/bittorrent-sync/id665156116?...
https://play.google.com/store/apps/details?id=com.bittorrent...