Krunner is a multi-function command line menu for the KDE Plasma Desktop.
At times, it almost seems as you could manage all your computing from Krunner. Among other things, you can launch commands, open websites using the abbreviations defined in System Settings > Shortcuts > Web Shortcuts, send emails, convert units of measurements, open particular system settings, and view the date and time.
Krunner is amazing because it's an incredible search tool that more than likely already comes with your standard KDE installation.