BitTorrent Sync, a new piece of software that operates like Dropbox in that it syncs files on different systems, has been released to the general public in its unpolished Alpha form. BitTorrent Sync makes use of the BitTorrent protocol to sync files across different systems without the need for a centralized server.
The best part is that it does all of this for free. There's no need to pay for a centralized server to host your files or manage the syncing. There are some downsides to not having a central server, but for the most part, BitTorrent Sync fills a much needed gap. You can check it out at BitTorrent Labs.