macOS

I have two identical WD Passports 1TB external disks - one orange one yellow (crucial information :D). On one of them, I store all my data - design files, family pictures etc. Second one, I used to use as a backup. Before formatting my macos I had an app that worked like that: I would plug both of the to my macbook, after clicking a button, it would compare orange and yellow, and whatever was on orange but was missing on yellow, it would copy that file to yellow. I could set it up, that if something was missing from orange, but was on yellow, it would also delete it from yellow (or if I wanted, it would leave it there). Now, for the love of me I couldn't remeber what it was called. It was very basic looking...

Any idea what it was, or maybe a suggestion for a similar app? It was deifnitely 100% free.

EDIT: I remember that backup option were presented like this A>>B, A=B etc.