How Many Different Ways Are There To Force Quit An Application?
There are many ways to force quit an OS X application:


Press and hold Command-Option-Shift-Escape for a few seconds. This will force quit the active application.
Press Command-Option-Escape to bring up the Force Quit window, where you can select the application you want to force quit.
Option + Right click on the Dock icon of the application and select Force Quit.
Click on the Force Quit menu option in the Apple menu to open the Force Quit dialog.
Hold shift and click on the Force Quit menu option in the Apple menu to force quit the active application
Use the Activity Monitor to force quit applications
Use the terminal to kill the process: killall safari will kill all Safari processes.


Source: OSXDaily