Option + 3 or alt + 3
If you put a lot of demand on your Mac, as many of us do, you may see applications become unresponsive or ‘frozen’ often coupled with the colour wheel slowly ticking away. In severe cases your dock may become sluggish, or stop responding altogether. Mac OSX has a number of ways to deal with stalled apps.
The quickest method involves using the ‘Force Quit Applications’ window built into OSX.
But what if I have an unresponsive Mac and can’t click the Apple logo?
Do not fear, this is where the keyboard shortcut may save the day. You can open the Force Quit Applications window pressing Command + Option + Esc simultaneously.
Select the problem application which often displays “(Not Responding)” next to the name, then click the button titled “Force Quit”
Okay, but I just want to force quit the front-most application
No problem. You can force quit the front-most application pressing Command + Option + Shift + Esc simultaneously.