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
Bacula is designed for enterprise-level backups with extensive features and scalability, making it suitable for large data sets, while Unison is focused on real-time file synchronization and is ideal for smaller data sets and simple setups.