The Gatekeeper Before I forget what I learned today, I better write it down. Gatekeeper on macOS ensures that properly signed and authentic apps and other executable files, including dylibs and kexts, are executed on your Mac. But if you want to execute an open-source tool installed by brew or some other way on your machine, you will usually see something like this confirmation dialog. In this case, for an app FSNotes installed with brew.