open source
https://backuppc.github.io/backuppc/
https://www.zmanda.com/lightning/
http://luckybackup.sourceforge.net/
http://0pointer.net/blog/casync-a-tool-for-distributing-file-system-images.html
https://github.com/bit-team/backintime
https://github.com/teejee2008/timeshift
https://github.com/spersson/Kup
https://github.com/lelutin/backupninja
http://kbackup.sourceforge.net/
http://www.diffingo.com/oss/fwbackups
https://wiki.ubuntu.com/TimeVault
Reference
https://opensource.com/article/19/3/backup-solutions
https://www.ubuntupit.com/top-15-free-open-source-backup-software-for-linux/