Is there a shortcut to close all Modern UI apps at once from the Desktop?
I tried killing
RuntimeBroker.exe but it didn't work.
Go to PC Settings (open Charms bar, click on Settings and then click on Change PC Settings) and click on General, you’ll see an option under App Switching called Delete History.
Clicking it will clear all app history, including killing the running apps.
On Windows 8; all "modern" applications seem to be dependent on explorer.exe. Restarting the process from Task Manager seems to stop all Windows 8 (modern) applications.