Press Command + Option + Esc
Select the app
Click Force Quit
Click Force Quit again if prompted
Right-click the app in the Dock
Hold Option
Click Force Quit
Open Apple menu
Click Force Quit
Select the app
Click Force Quit
Open Activity Monitor
Select the app
Click the X button
Click Force Quit
Use Terminal
Run `killall AppName`
Use Terminal
Run `pkill AppName`