It's pretty simple, mostly comprising circuitry to interface devices to a PC parallel printer port, most of the work is then done in software.
It appeared to be an 'open' design I could build one from scratch, buy a PCB and assemble it or buy a complete one. Something I liked was the availability of circuit diagrams and (I think) the source code for the software. I've known about the Willem Programmer for several years but never got around to buying or building one.
