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 hosts (or different disks on the same host), modified separately, and then brought up to date by propagating the changes in each replica to the other. Developed by Benjamin C. Pierce
License: Open Source
Unison is best for users needing real-time synchronization and version control across multiple platforms, while FreeFileSync excels in ease of use and flexibility with various sync modes, though it lacks real-time capabilities.