SlackBuildsOrg/system/FreeFileSync

FreeFileSync is a folder comparison and synchronization software that
creates and manages backup copies of all your important files.
Instead of copying every file every time, FreeFileSync determines the
differences between a source and a target folder and transfers only
the minimum amount of data needed. FreeFileSync is Open Source
software,available for Windows, Linux and macOS.

Notes:
I)  This package installs to /opt/FreeFileSync


II) The original binaries are hosted on the package maintainer
    github due to the the fact that the FreeFileSync web server is
    causing problems with SlackBuilds CI/CD environment.
    If in doubt please compare the md5sums.