Code:
try
tell application "System Events"
set listOfProcesses to (name of every process where background only is false)
set noFinder to listOfProcesses's (items 2 thru -1)
end tell
repeat with x in noFinder
quit application x
end repeat
end try
Then to set a keyboard shortcut, simply build a service using Automator or use Shortcuts and add it to your menu bar and set a keyboard shortcut.
Mine is CMD-F19