Program Manager had quite the run. It was included in versions up to and including Vista. I took a quick look for progman.exe on Windows 10 but looks like they stopped shipping it.
I set it up with Ctrl+Shift+Space as a hotkey so it's easy to open. I have about two million files on my C: drive. When I open Everything it displays them all, and then as I start typing in the search box it filters the list as fast as I can type. Highly recommended!
It just searches filenames, not content, but often that is enough.