If you’re a Mac user of some length of time or experience, you know that there are a ton of keyboard shortcuts laced throughout the operating system. In addition, every application you run on your Mac has a ton of these same shortcuts.
One easy way to see them is to click on a menu in a running application. To the right of each menu command, you’ll see the Keyboard shortcut for that particular menu selection. For example, clicking on the Edit menu in most applications on the Mac will give you the Cut (Command-X), Copy (Command-C), and Paste (Command-V) shortcuts.
There’s an easier way, however, to see all the application’s associated keyboard shortcuts, in the form of an application you can download right now.
CheatSheet, an app by Media Atelier, is an app that runs in the background on your Mac. In any application, holding the Command key down for a couple of seconds will bring up all the shortcut commands available to that app in a big visual menu.
Download the app from the developer website and move the application to your Applications folder. If you don’t and try to double click on it, OS X Lion will kindly tell you it has to run from Applications, and would you let it move it for you. So nice! Tell it yes, and then you’ll see the prompt that shows you how to activate CheatSheet by holding down the Command button.
In any application, now, hold the Command key down and you’ll see all the keyboard shortcuts available to you in that app.
Source: CheatSheet App
Via: OS X Daily