rsync is a utility for efficiently transferring and synchronizing files across computer systems, by checking the timestamp and size of files. Developed by Wayne Davison
License: Open Source
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
Rsync is primarily focused on one-way file synchronization with high efficiency, making it ideal for backups and mirroring. In contrast, Unison excels at bidirectional synchronization, allowing users to seamlessly collaborate on files across multiple locations.