The Nintendo Vs. Series was a series of previously single-player NES games which had been adapted to provide multiplayer. All games in the Nintendo Vs. Series were released for an arcade system titled the Nintendo Vs. System, although it is also known as the Vs. UniSystem of the Vs. DualSystem. A wide variety of games were released into the Nintendo Vs. Series, mostly because they were cheap to port and manufacture, making them popular among arcades.
Typically, the games utilizing dual monitors, although some cabinets used a special monitor that allowed for the game to be played on different "screens." Besides a few minor differences, most of the games in the Vs. Series ran on the same hardware, although some games differed in the video chip used (video chips change the palette). As such, the only thing different between the cabinets were the ROMs inside the cabinet, and the video chip. The ROM can still be switched out, although the video chip will display inaccurate colors.
Although most games stayed essentially the same as their NES counterparts, some games were altered drastically. Vs. Super Mario Bros. included levels from Super Mario Bros.: The Lost Levels, and Vs. Duck Hunt had upgraded graphics and an extra bonus stage.