I have used various open source alternatives for file syncing that needed more development before being released. That being said Bittorrent Sync has NEVER let me down. It's easy to run and install thanks to the new GUI offering, and Bittorrent Sync allows me to transfer huge video files quickly from machine to machine without wasting time syncing stuff to the "cloud."
I've also found it to be a fantastic way to share large files easily with others, while maintaining IP address and directory privacy along the way. Despite the numerous alternatives available, I remain firmly grounded as a Bittorrent Sync fanboy.