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.
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.
"Last week, I told you about my NAS purchase, and my desire to explore desktop applications for backing up your Ubuntu computer. From the administrative interface of my Buffalo NAS, I created a network share that I could access with the different systems in my office. It's an SMB share so that it can also be accessed from Windows if needs arise. I then permanently mount those shares as network file systems (though not NFS) on my Kubuntu Karmic system. This I do from the command line