Audio and Video Switchers
Manufacturers Sold: Extron, Kramer, Sierra Video

Switchers enable multiple video and audio signals to be selected and sent to one or more display devices. For example, to view two computers with separate presentations, a switcher would be used to physically connect both of the inputs to the display device.  The switcher would then be used to select or "switch" between the two computer presentations, allowing the user to alternate back and forth.