AppKiller lets you close all your open apps, with the fuss of going through them one-by-one. Do you want to be able to do with a single click? Or – even better – with a single… keyboard shortcut? Look no further!
Features

Easy-to-use: App Killer sleeps unobtrusively in your status bar and waiting for… orders
Ultra-fast: Killing all your open application will take no more than… milliseconds
Cmd+Shift+K: And that’s all it takes to instantaneously kill all your open apps–really!

WHAT’S NEW

Version 2.1:

Added support for OS X 10.7
Minor tweaks

REQUIREMENTS

OS X 10.7 or later, 64-bit processor