Ancient black and white technology superseding the MDA system.
The Hercules display system was one of the earliest methods for attaining dual display support on your computer before the advent of dual VGA cards. Some software applications (such as the Borland TurboPascal IDE) allowed for dual display support, displaying the code on one screen and the execution on a second colour screen.
Supported resolution
These display adapters occasionally came with other interfaces built onto the card such as a parallel or serial port.
To quote the 
PCGuide
"One weakness of the original MDA display was that it did not support graphics of any kind. A company named Hercules created in the early 80s an MDA-compatible video card that supported monochrome graphics in addition to the standard text modes.
The Hercules card was actually a very widely-accepted standard in the mid-80s; eventually Hercules clones even appeared on the market. Support for the card was included in popular software packages such as Lotus 1-2-3 to allow the display of graphs and charts on the computer screen. It has of course been replaced by later, color, graphics adapters."
GerwinVanDeSteeg might still have one somewhere, along with a working screen.
Superseded by CGA
