Exactly what I was looking for

I am a photographer using a MacBook Air. I store my original master DNG files on a portable external hard drive, and my Lightroom catalog on my computer’s SSD drive. My wife, also on a Mac notebook, stores our family snapshots in an iPhoto database on a separate external hard drive. I’ve set up three tasks, one that makes an incremental backup of my wife’s iPhoto library to a folder on my Lightroom external HD, one that makes an incremental backup of my Lightroom HD to a folder on my wife’s external drive, and one that backs up my Lightroom catalog folder on my computer to my wife’s HD. Hook the two drives up to my computer, click one button and everything synchronizes… and both my wife and I have up-to-date access to all of our pictures.

This app is _powerful_ so read the help webpage carefully. The interface could help you more in understanding the coding symbols, so pay attention. The drag and drop functionality to fill in file path names sometimes stops working for no apparent reason, but does not affect the the working of the app. When you drag a file onto the input/output fields, you are told it is advisable to save a com.greenworldsoft.syncfolderspro file. Nowhere is it explained in the documentation what this file does, or where it ought to be saved. In fact, saving it seems to do nothing at all, as the file does not appear in the finder location you target. It does not appear that either saving or canceling at this point makes any difference to the proper functioning of the app.

Aside from these niggling things, this app is exactly what I was looking for.

malaca about Sync Folders Pro