It's called checkoff's gun because when you write a play you're supposed to make a list of all the props and check off the ones that you've used in the plot, to make sure you don't miss any.

Hi I'm Dana, I mostly just tool around with friends, play RPGs, and listen to podcasts, but I've also been known to make podcasts at SuperIdols! RPG and I've written a couple of short rpgs at my itch page and on twitter.
It's called checkoff's gun because when you write a play you're supposed to make a list of all the props and check off the ones that you've used in the plot, to make sure you don't miss any.