It sounds like Unison (which I have never heard of, actually ...) shares a lot of ideas with Microsoft SharePoint.

(Which, by the way, is an excellent tool which proves once again that The Evil Empire™ can write good stuff).

i know this thread is 3 years old. But I really want to reply to this thread as it is giving people the wrong perception of unison. It is the reason why unison is underrated and that it is no longer in development.

I uses unison to sync between 2 servers. It does 2 way sync without needing to run it TWICE as shown by someone's reply here. You only need to run it ONCE unlike rsync and it will sync both way. It is a very good tool. Think of it as a better rsync. The reason it is not as powerful as rsync is because of it's short development days. If only it was continually developed, it would have blossomed into a full fledge competitor to rsync.

I still uses it now and it works for what I need which is 2 ways sync at one go. And it is as fast as rsync can be.