Package xcape

Use a modifier key as another key when pressed and released on its own

https://github.com/alols/xcape

xcape allows you to use a modifier key as another key when pressed and
released on its own. Note that it is slightly slower than pressing the
original key, because the pressed event does not occur until the key is
released. The default behaviour is to generate the Escape key when Left
Control is pressed and released on its own. (If you don't understand why
anybody would want this, I'm guessing that Vim is not your favourite text
editor ;)

General Commands
Command Description
xcape use a modifier key as another key