QuitsAppsMBI is a menubar app that can be used to quit all currently running apps at once, or just one at a time.
When you launch this app its menu is populated with the names and icons of all currently running apps on your Mac.
Select the menu item "Quit All Apps" to quit every app. Since this is achieved in the usual way, any app with unsaved documents will alert you asking if you want to save changes.
After you quit any app or all apps, a menu item named "Relaunch" appears. Select this menu item to relaunch the app or apps.