There are alot of old CNC’s out there that this maybe a good way to “upgrade” them. In the 1990’s CNC for metalworking where coming of age, problem was most of them never got updates, so they are still running Windows 98, or …horrors, MS-DOS. They are also very limited (maybe 25 lines of gcode at a time for example). This could be a way to upgrade those machines to keep them going. The author’s reasoning here was to convert from using a controller that ran on a parallel port to USB.
http://www.instructables.com/id/Converting-CNC-Electronics-to-Arduino/