Syncthing

Syncthing is a continuous file synchronization program that keeps files in sync between two or more computers in real time. It is decentralized by design: there is no central server that might be compromised, and none of your data is ever stored anywhere other than on your own devices.

Every device is identified by a strong cryptographic certificate, and only devices you have explicitly approved can connect. All communication is secured with TLS and perfect forward secrecy, so files are protected against eavesdropping and tampering as they move directly between machines.

Syncthing is built to be safe from data loss, automatic, and easy to use for individuals. It runs on Windows, macOS, and Linux with GUI wrappers and Docker support, and ships a built-in automatic upgrade mechanism. It is open source under the MPLv2 license.