FolderWatch is a native Mac OSX App that watches the filesystem for changes and then runs a script of your choosing. Multiple folders can be configured to be watched, each with their own script to be run when changes occur. The original use case for this tool was to allow someone to edit files locally and then have them automatically copied up to a server (via an rsync script) where the changes could be previewed on a website. That said, the tool could be used for anything that requires a script to be run in response to some filesystem change. This tool was developed because we couldn't find any readily available equivalent on the interwebs for OS X. If you need something like this on Windows, Winscp will likely serve you well.
An example bash script that uses rsync to move files between boxes is available in