The launcher built into the KDE Plasma desktop. While its basic function is to launch programs from a sort of mini-command-line, its functionality can be extended by "runners" to assist the user to accomplish a lot of tasks.
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Pro Extensible with plugins
Krunner can be extended with the use of "runners" which are essentially plugins for the app launcher to allow for extra functions.
As it is written in Qt QtQuick using QML.
Pro Can be used to open websites
By just typing an URL into the text box users can have the site open in their default launcher.