"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)..."