[BBLISA] Live Sync / Backup / Sync without crawling

[Edward Ned Harvey]

Hey, anybody know of any program, which can sync or mirror a directory, without the need to scan the directory?  For now, I'd be happy to find *any* such program, for whatever OS.

I know it can be done, via things like inotify, FSEvents, or FindFirstChangeNotification ...  

Take a really simple hypothetical example.  Suppose I want to rsync some dir to some foreign location periodically.  At present, every program I can find needs to crawl the local dir (or worse) to see what's changed.  But with inotify etc, it's possible to have already created a list of what's changed, and simply mirror the changes rather than doing the whole tree crawl.  This would be super useful for syncing a large directory.