I take a lot of screengrabs for work. A lot. And sometimes, I need those screengrabs to be layered PSD files so that I can move items around and not worry about what's in front of what or where any particular window is located. I used to use an app called Layers to do this but it looks like its abandonware now so I went in search of another.
I found this: ScreenShot PSD. It's also a bit dated (last updated in 2012) but it seems to do the job just fine and at least it's on the Mac App Store for free. Can't beat that I suppose. Glad to have this type of app back on my computer.