What the heck is it for, you ask? It is specifically to connect a CMD HD to a CMD RAMLink. As far as I can tell, that's it! And that's why they are so hard to find.
CMD's parallel port uses a very unique and difficult to source 14-pin rounded cable.
From the HD's User Manual:
HD users desiring even faster performance with the HD can easily boost data transfer speed to the maximum attainable level while retaining compatibility.
There is one guy in the UK on Ebay building these new, but apparently he's making them out of gold.
I got this NOS specimen from someone in Canada after hunting around and sending emails to several people I thought might at least have 1. Luckily, one gentleman I contacted had a couple and was willing to sell one of his original stock (for less than British gold).
Connecting my RAMLink and CMD HD will finally come to fruition! That being said, it doesn't sound like a plug-and-play situation by any means. I've got some software management and updating to do.
From the RAMLink manual: I need to double-check but I think the HD DOS version my drive came with is 1.12.
I have the original RAMLink utilities disk. I'll need to create some disks from this excellent repository next for the HD. Some of the utilities for it sound very cool. Zoom floppy to the rescue!