This page: http://googleappsupdates.blogspot.de/2012/06/apps-script-in-docs-list.html says
Google Apps Script projects are now included in the docs list in Google D
I'm afraid there is a small misunderstanding here... the script itself can be created as a standalone document in the drive's doclist, not the executable macro, these are two different things.
What you refer to is an url that points to the server and starts the execution of a script. What the documentation says is that the script (which is an editable text file after all) doesn't need to be included in a site or in a spreadsheet but can exist as a new document type.
Sorry for being redundant but I wanted to be sure it was clear enough.
EDIT (following your comment) : you are right : if you created the script in a spreadsheet "container" it doesn't appear as a standalone script file. It does only if you create it independently.
That said, I think the easiest way to have fast access to webapp is to create a shortcut in the Browser itself, a so called bookmark or favorite (depending of your Browser)... at least this is how I do :-)
And it's not an issue to send such a link by email since you don't have to type it ...
Today, 2018-1-11, Google launched the Apps Script Dashboard. It list all the script project files, standalone and bounded.
Reference
This is a great question, and I would like to direct you guys to this link in the docs that explains the difference between a bound and an unbound script. I found a great script that someone shared and I wanted to make a backup of it, but could not find it in Google Drive even after saving his spreadsheet that was using the script. Turns out it was a bound script, and that is perfectly normal.
So I am either going to create a new project and copy and paste the script, OR maybe do it right by making another copy of it that will hopefully show up in all my sheets when I go to Tools>Script Editor.
(Edit) I copied and pasted the code into a new project. But before I did that:
First open up a new Google script at https://script.google.com.
From there, you can click File --> Open.... This will bring up Google Drive in a window, but with the special search already in the search box: "type:script".
You can go directly to it here: https://drive.google.com/drive/u/0/search?q=type:script