An ancient black and white video graphics adapter superseding IBM's MDA. In addition to the 80x25 text mode, programmers could also take advantage of a 720x350 pixel monochrome graphics mode. These display adapters occasionally came with other interfaces built onto the card such as a parallel or serial port.

PCGuide says :
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 It has of course been replaced by later, color, graphics adapters.

Neither the later designed CGA standard nor its successor, the EGA, managed to eclipse Hercules. CGA only offered abysmal resolution (and hence, display quality), and the EGA text modes did not match the quality of a Hercules card either. Only with VGA did an adequate standard emerge that could replace Hercules in all respects.

Nevertheless, Hercules compatible cards remained popular particularly among programmers, because they could be used alongside a graphics card of the aforementioned standards, in effect offering one of the earliest methods for attaining dual display support on PCs. While few end user applications took advantage of this, Borland developer applications (such as TurboPascal) were capable of displaying the IDE on the Hercules screen while the program being written would run on the primary display adapter. Some other applications had similar support for secondary Hercules displays.

(GerwinVanDeSteeg might still have a Hercules somewhere, along with a working screen.)