Syncthing 
replaces proprietary sync and cloud services with something open, trustworthy and decentralized. Your data is your data alone and you deserve to choose where it is stored, if it is shared with some third party and how it's transmitted over the Internet.
Setup
# Add the release PGP keys: curl -s https://syncthing.net/release-key.txt | sudo apt-key add - # Add the "stable" channel to your APT sources: echo "deb https://apt.syncthing.net/ syncthing stable" | sudo tee /etc/apt/sources.list.d/syncthing.list # Update and install syncthing: sudo apt-get update sudo apt-get install syncthing
Copy the template from the example systemd service file and copy them to /etc/systemd/services/syncthing.service
On Raspberian, I stopped errors by installing policy kit using `sudo apt-get install policykit-1`
sudo systemctl enable syncthing
sudo systemctl start syncthing