Smoothstepper Pro OEM
I saw this on the Mach3 forum. CNC-Steuerung has a new Industrial version of the Smoothstepper. It adds a lot of I/O filtering and safety circuits. The Smoothstepper is a USB motion controller that runs as a Mach3 plug-in.
I use one on my router. In general, it works quite well, but beware that their support is basically non-existent. You are on your own to figure out problem and updates are on a slow schedule. Pretty soon the parallel port is going to go away so we will all be using this type of thing.