Unison File Synchronizer is described as 'Unison is a file-synchronization tool for POSIX-compliant systems
(e.g. *BSD and GNU/Linux), macOS and Windows, with the caveat that the
platform must be supported by OCaml. It allows two replicas of a
collection of files and directories to be stored on different hosts
(or diffe' and is a popular File Sync tool in the backup & sync category. There are more than 50 alternatives to Unison File Synchronizer for a variety of platforms, including Windows, Mac, Linux, BSD and iPad apps. The best Unison File Synchronizer alternative is Syncthing, which is both free and Open Source. Other great apps like Unison File Synchronizer are FreeFileSync, Resilio Sync , rsync and Beyond Compare.
Unison is birectional and can used a server client infrastructure. Freefilesync is mostly unidirectional and there is no server possibility.