Introduced In: 10.3 "Panther" (2003) 

Power users and clutterers alike welcomed the addition of Exposé. Gaining the ability to quickly take stock of how many windows you have open, and seeing a real-time thumbnail of that window was groundbreaking. And it was customizable. You could make it so you only saw windows of a certain application window, all windows, or you could clear your entire screen for a hot second to take a breather. Of course, Microsoft tried to bite and introduced a feature called Windows Flip 3D, but we all know where we saw it first.