xset is an X.org command line utility. A bunch of interesting things can be done with it:

Tweak the mouse sensitivity or accelleration on the fly

xset m (accelleration value)

Turn the system bell off temorarly

xset b off

Manually switch off the display / Force the display to go on standby now

xset dpms force standby (or suspend or off)

Manually activate the screen-saver

xset s activate