In short
It is a light desktop app (Windows and iOS), so it works with any screen sharing or recording tool. Skype, Twitch, Zoom, Meet, Teams, Discord, Camtasia, Facebook or YouTube lives… all of them!
A quick keyboard shortcut (alt+M or option+M) brings you a pop-up window in which you can start typing a full-screen message to anybody that looks at your screen. The app waits in the background until you call it.