I've been using BitTorrent Sync with a windows pc and an android tablet. What I like about it is that file/folder changes made in one are made in the other--automatically. With, say, dropbox, if I put a file in my pc dropbox folder, I can only 'see' it on my tablet, unless I deliberately download it to the tablet dropbox folder. There is no off-line access to files unless I download them. It's not really auto-syncing as I would define it. BitTorrent Sync is brilliant in this regard; is it unique?