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.
Unison shares a number of features with tools such as configuration management packages (CVS, PRCS, Subversion, BitKeeper, etc.),distributed filesystems (Coda, etc.), uni-directional mirroring utilities (rsync, etc.), and other synchronizers (Intellisync,Reconcile, etc).
Unison runs on both Windows and many flavors of Unix (Solaris, Linux, OS X, etc.) systems. Moreover, Unison works across platforms,allowing you to synchronize a Windows laptop with a Unix server, for example.