I recently starting using Bittorrent Sync, a new alternative to Dropbox and Google Drive that does not put a copy of your files on a central server. Instead, your files are synchronized between your devices using the peer-to-peer Bittorrent protocol. Bittorrent seems to be secure, is very fast, but, unfortunately, Bittorrent Sync is not open source.
For the last several years, I have used Dropbox as my primary file synchronization program, and Google Drive as my backup. Both programs are great, but both had a few deficiencies that kept me looking for alternatives. For example, Dropbox is fantastic, but your files do sit on someone else’s server, albeit in an encrypted form. With Google Drive, your files sit unencrypted on Google’s servers, but the recent NSA debacle may encourage Google to start encrypting the Google Drive hosted files. The big strike against Google Drive, however, is that it has no native client for GNU/Linux.
rest here