Is this the simplest Progressive Web App ever? It's just a black browser tab / window / screen, but it can help you focus, rest your eyes, manage screens, test PWAs, or serve as a presentation background or privacy screen. Really?

An application that displays a full-screen window in pure black for the Windows operating system. Exit can be initiated by simply pressing any button.

Black Screen Helper

Mouse activated backup for when the screen dies

Take Screen Shot With Black Screen App !