It's not OSS, but Far Manager purports to be a way to keep sets of files in multiple locations synchronized. The WinSCP site claims that it's "shareware." I don't see that they're charging for it, but I don't see that source code is available, either. If I used Windows and hadn't figured out how to make rsync work, I'd definitely give this a shot. Oh, someone has made a newer, and presumable better packaging rsync for windows called cwRsync. I'd check that out too.