Yes, Windows has it by default, why not Mac? Well you can always push F11 to view the desktop, but what if you want a dock icon to do this? easy..

Open Apple Script Editor (Machintosh HD > Applications > System Utilities > Apple Script Editor)

Choose File > New

in the code window type

(* AppleScript Show Desktop *)

activate application “Finder”

do shell script “/Applications/Utilities/Expose.app/Contents/MacOS/Expose 1″

so you now have something like this:

Save this. File > Save As – “Show_My_Desktop”, change File Format to Application, check the Options box “Run Only”

Save

If that works you will not have an icon on your desktop like this:

Drag this into the dock, then click it. All done.

If you want it to look a little better, then change the icon. To do this read my previous post Change An Icon in Mac OSx