I recently developed the need to find a program that kept my USB drive synchronized with it's backup folder on my laptop's hard drive. Sometimes I work on the files in the backup folder if my USB drive isn't available, and vice versa... so I need to be able to keep both up to date.

SyncBack lets you create a profile for different things you want to back up and/or synchronize. It'll let you run a simulation before the real thing so you can see what will happen beforehand. It'll also overwrite either location's older files with the newer updated one. It'll show you which files it's overwriting, and the dates of the older file and newer file it's being replaced with.

For somebody who uses their USB drive to work wherever, this program is a lifesaver. That way you can work on the files on your computer at home and away on the USB drive, and keep them both updated. I mainly use the files on my computer at home for a backup but sometimes if I don't have my USB drive on me, it's nice to be able to work on files on my backup folder at home knowing I can update the USB drive with a click of a button, and vice versa.