BitTorrent Sync has had a similar feature for a while now. <a href="http:&#x2F;&#x2F;help.getsync.com&#x2F;hc&#x2F;en-us&#x2F;articles&#x2F;204754669-What-is-a-BTS-file-" rel="nofollow">http:&#x2F;&#x2F;help.getsync.com&#x2F;hc&#x2F;en-us&#x2F;articles&#x2F;204754669-What-is-...</a>