Workspace window.

What about ctrl + right click to show shell menu?
Making it an option could help save time.

an interesting idea, but is it not quite intuitive?

Actually, it's intuitive but when you use shell menu frequently it becomes annoying.
Holding left control might be an option for displaying shell menu.

probably, you misunderstood me

Suppose we run PhpED and opened Explorer tab (docked window).
It's where you can select files and/or directories. It allows for example to select multiple files and delete them.
How would you do it? Certainly, you press Ctrl and click the files one by one or select first one the select the last one while holding down Shift- key. So Ctrl and Shift are already used in Multiple Selection function .
In the example above, Ctrl and Shift work together with Left mouse button clicks.
Regarding the right one, it also selects what you're clicking on, otherwise it would confuse much and again if Ctrl or Shift are used, it allows to add files to the previously selected ones.
Remaining Alt, can't be used at all because it conflicts with System menu (just try to invoke any popup anywhere while holding Alt )
So... I think neither Ctrl nor Shift are quite intuitive for invoking Shell menus.
Any futher ideas?

Well, you are absolutely correct.
All I can propose is making it an option
when user can choose if ctrl + rclick
works for selecting or for shell menu
call.

well.
Let's image that the following content is in the tree where you're going to click on:

file1.php
file2.php
file3.php

suppose, file3.php is a matter of your interest through the Shell
suppose file1.php was selected before and threrefore it's shown with blue background.
now, you right-click on the file3.php while holding down Ctrl key. Isn't it expected that file3.php will be selected? (at least I'd expect it)

By turning off "selecting with R-Clicks", we will get file1.php selected ans shell menu called against file1.php It will be quite confusing. Right?

If we do not turn off "selecting with R-Click", we'll get both file1.php and file3.php selected and Shell menu will be invoked against the two and it still will be quite confusing.

There is a 3rd way, of course. Do not leave file1.php selected with R-clicks and select only file3.php, but it will be unclear how to get multiple files selected

Thanks for implementing!