superkey-launch allows you to open KRunner in KDE using the Super key as well as the app launcher in XFCE, Mate, Fluxbox and several other environemnts. If you hold down the Super key it will still act as a modifier key, allowing you to use it for other keyboard shortcuts. superkey-launch is desktop agnostic. superkey-launch is a small application that runs in the background as a daemon. It was forked from xcape by Albin Olsson: https://github.com/alols/xcape