In both Windows and Gnome, the Super key (the one with the Windows icon) can be used as a shortcut, e.g., to open the application launcher. Very handy. Unfortunately, in KDE, the key is restricted to only be used as a modifier. There has been a long discussion about this since 2009, and the outcome is yet unclear. For the time being, Hans at hanschen.org has created ksuperkey. It is a very small & simple tool which you include in your auto-startup settings, and it will make the Super key send ALT+F1, which is the default shortcut for the application launcher.