Is "Quit others" possible?
Using the SO answer referenced by Diago, maybe something like the following modification can exclude the currently active application:

tell application "System Events"
    set the visible of every process to true
    set app_name to name of the first process whose frontmost is true
end tell
set white_list to {"Finder", app_name}
try
    tell application "Finder"
        set process_list to the name of every process whose visible is true
    end tell
    repeat with i from 1 to (number of items in process_list)
        set this_process to item i of the process_list
        if this_process is not in white_list then
            tell application this_process
                quit
            end tell
        end if
    end repeat
on error
    tell the current application to display dialog "An error has occurred!" &amp; return &amp; "This script will now quit" buttons {"Quit"} default button 1 with icon 0
end try


Then you can add this as a service using Automator, and assign a keyboard shortcut for it in the Keyboard section of System Preferences.