Exposé, one of the built-in Mac gimmicks that Windows doesn't have, has been doing great job on promoting Mac to Windows users. Personally, I will invoke my Exposé whenever I saw my Windowish friends approaching me while operating my Mac. It's just "Wow!" for them, though it's as simple as bread and butter for Mac users.
Besides being used for attracting attention, we, Mac users, usually use Exposé for the sake of productivity boosting.
[Default Shortcut: F9]
[Default Shortcut: F10]
[Default Shortcut: F11]
There is a possibility that you've changed the keyboard shortcuts previously, if you want to revise shortcuts to invoke those Exposé, go to System Preferences… ▸ Exposé & Spaces ▸ Exposé.
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