Exposé (macOS)
Panther's window overview from 2003: one press of F9 and every open window shrinks into a tidy mosaic — the effect that showed what a compositor was actually for.
Mac OS X 10.3 Panther, October 2003, claimed three keys: F9 showed all windows shrunk and laid side by side, F10 only the active application's, and F11 swept everything aside to reveal the desktop. The windows kept updating while shrunk — a film carried on playing in its little tile — which was possible because Quartz Compositor already held every window in a buffer of its own. It was the clearest demonstration yet that compositing was good for more than shadows and transparency, and hot corners put it within reach of the mouse.
The imitations came quickly: Compiz's Scale plugin in 2006, KWin's Present Windows in KDE 4, the GNOME Shell overview in 2011 and eventually Windows 10's Task View. At Apple, Exposé was merged with Spaces and Dashboard into Mission Control in 2011; the name survives in App Exposé, a three-finger swipe down that shows one application's windows. The clash between those F-keys and the brightness and volume keys on laptops is one reason the fn key ended up so busy.