The SPLITMUX® DVI/VGA Quad Screen Multiviewer allows you to simultaneously display video from four different computers on a single monitor. Additionally, it can switch one of the four attached computers to a shared keyboard and mouse for operation and to four additional USB devices.
SPLITMUX-DVI-4 Device Control Protocol
SPLITMUX-DVI-4(RT) PDF Data Sheet
VGA Monitor Cable - Male-to-Male - $2.30
DVI-I Male to VGA Female Adapter - $12.00