Full Name: Duplicati
Open source?: Yes.
"Duplicati is free software and open source. You can use Duplicati for free even for commercial purposes. Source code is licensed under LGPL." - Quote from there website
Website page:
https://www.duplicati.com
GitHub page:
https://github.com/duplicati/duplicati
Latest release page:
https://github.com/duplicati/duplicati/releases
"Duplicati is a free, open source, backup client that securely stores encrypted, incremental, compressed backups on cloud storage services and remote file servers." - Quote from there Github