I'm new to OSX and the thing I miss from Windows 7 is the ability to open a new window if you hold the Shift key and press on the Applications icon within the task bar.
Similarly, OSX does have a function where if you press the middle button (the scroll wheel button), it does open a new window.
I have not stumbled upon a way to do it with the Keyboard and Touchpad.
Command + Click App Icon opens a finder window where the .App is located.
Control + Click App Icon is similar to secondary click.
Option + Click App Icon triggers App expose.
I am aware that Command + N opens a new window in most applications, however when working in multiple desktops, having a similar functionality to the middle button click with just the touchpad would be much easier.
5 Answers
My suggestion to you is learn how to use Apple-Tab to switch between apps. Shortcut keys are your ticket to speeding things up: Apple-Tab, Apple-N and your new window pops up. That assumes you are right handed and have your left hand available for shortcut keys, that is.
OP states that they work in multiple desktops, in that case for this approach to work, you want to turn off the automatic switching to the space where the Application is active. This will allow for opening a new window in the current desktop ("space"). System Preferences -> Mission Control -> uncheck 'When switching to an application ...'
BetterTouchTool (freeware) enables creating a shortcut that can be performed anywhere that sends a different shortcut to a specific application. Just have it send ⌘N to whatever program you want to open a new window in.
I downloaded and installed magicprefs, which allowed me to add more gestures onto both my trackpad and magic mouse - and it's free!
Then I downloaded HyperDock. It's got a 15 day trial, then it's $9.99US. Open HyperDock in your settings, goto Dock Items: by default there should be a Command + N Action, and the event is set to Middle Click. If it's not set, you should set it manually.
Now I can perform a 3 finger click to imitate the middle mouse button (which opens a new window on already opened applications)
3Ctrl-Click the icon on the dock should do the job. I have tried it with "Numbers", "Safari" and "Finder" with a track pad but it should work similarly with a mouse.
1HyperDock has this feature. After installation, go to the "Dock items" tab, select "All Dock items" and change the shortcut associated to "⌘ + N (New window)" from "Middle click" to e.g. "⌘ + Left click".
HyperDock has a 15 day free trial.