Once upon a time, there was a great product called BitTorrent Sync. It allowed you to sync files between your devices — computers, phones and tablets; Windows, Mac and Linux, iOS and Android. It was released as a free preview in 2013. It wasn’t open source, but developers said: Never say never :) We still consider this option. The software used strong end-to-end encryption, so your files couldn’t be snooped on in transit or grabbed from a central server.