xkill

The xkill command in Linux has turned out to be one of the more useful commands for me. It's good to turn to when an application freezes up. Blogger Steven Rosenberg writes about it here.

In short:

"On the same window as the application you wish to kill, open a terminal window and type xkill at the prompt. Your cursor turns into a "X" that kills whatever you left-click with the mouse."