How to force quit a Mac application

Mac applications may sometimes crash, even though not so often as in Windows, and, when this happens, you can force quit them in several ways:

Pressing CMD/ALT/ESC: a list of active applications will be shown. Click Force Quit to kill one of them.
Pressing CMD/TAB: same thing. Press Q to kill any open application, after selecting it.
Using Activity Monitor (found in Application/Utilities): it lists the open applications and has a Force Quit option, too.
Choosing Force Quit after right-clicking the icon of the application in the Dock.