FreeFileSync is a free open source backup software which helps you compare and synchronize files and folders on Windows, Linux and macOS.

Duplicati is a backup tool, not a file sync tool.

SMPlayer is a cross-platform graphical front-end for MPlayer and forks of Mplayer using GUI widgets offered by Qt.

Unison is a file-synchronization tool for OSX, Unix, and Windows. It allows two replicas of a collection of files and directories to be stored on different ho…