How to map a key to go to desktop?

Question

Before you say anything, I know I can use win+d to go to desktop. I would like to be able to just use the windows key instead of win+d because I'm trying to replace the start menu and taskbar with rainmeter plugins, but I use the windows key for many tasks that I can now only use when on the desktop.

Answer 1

LWin up::
If (A_PriorKey = "LWin") ; LWin was pressed alone
    Send, #d             ; go to desktop
return

; In this case it's necessary to define a custom combination by using "&" or "<#" 
; to avoid that LWin loses its original function as a modifier key:

<#a:: Send, #a  ; <# means LWin

Answer 2

The following AutoHotkey script will intercept the Left-Win key, minimize all windows and activate the desktop, then set the Left-Win key to down. It will wait for the Left-Win key to be released to set it to the up state so it will work with future pressed keys in combination until the Win key is released:

LWin::                           ; intercept the Left-Win key
WinMinimizeAll                   ; minimize all windows
WinActivate, Program Manager     ; activate the desktop
Send {LWin down}                 ; send Left-Win down
KeyWait, LWin                    ; wait for Left-Win key up
Send {LWin up}                   ; set Left-Win key up

You may do the same with the right-Win key (RWin).

After installing AutoHotKey, put the above text in a .ahk file and double-click it to test. You may stop the script by right-click on the green H icon in the traybar and choosing Exit. To have it run on login, place it in the Startup group at:
C:\Users\USER-NAME\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup.