Unison is a file-synchronization tool for 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. Unlike simple mirroring or backup utilities, Unison can deal with updates to both replicas of a distributed directory structure. Updates that do not conflict are propagated automatically. Conflicting updates are detected and displayed. Unison can synchronize either locally (between volumes mounted on the same computer) or remotely,between any pair of machines connected to the internet, communicating over either a direct socket link or tunneling over an rsh or an encrypted ssh connection. It is careful with network bandwidth, and runs well over slow links such as PPP connections. Unison is available for both Windows (95/98/NT/2K) and Unix (Linux, Solaris). Moreover, Unison works across platforms, allowing you to synchronize a Windows laptop with a Unix server, for example.