Unison

Unison synchronizes two replicas of files and directories across POSIX‑compliant systems and Windows, allowing each side to be edited independently and then bringing them up to date. It propagates non‑conflicting changes automatically, reports conflicts for user resolution, and works over ssh or direct TCP while conserving bandwidth with rsync‑like compression. Because it copies data rather than mounting a network filesystem, the synchronized files remain usable offline and no kernel modifications or superuser privileges are required.

The tool can operate in a repeat mode that watches the filesystem and synchronizes shortly after changes occur, making it suitable for keeping data consistent between a laptop and a server, between different disks on the same host, or across heterogeneous platforms. Its design emphasizes resilience, leaving replicas in a sensible state after crashes or communication failures.

Unison is distributed under the GPL‑3 license, with source code and binary packages available through various Linux distributions and other packaging systems. Documentation, mailing lists, and a wiki provide support for users and contributors.