I'll start off with the money shot. It's a 35-key keyboard, probably originally intended for handheld inventory computers or something else used in an industrial setting. Pretty normal and what you'd expect, but check it out, doubleshot caps.
Now for the matrix:
This isn't a mechanical keyboard, and it's not really a rubber dome either. The best way to describe this would be 'metal dome', where a small disc of metal acts as both the spring force in the key and the contact. Very odd.
Above is the best evidence of where this keyboard came from. It's from AMP Inc., part number (maybe?) 26051. No, that pic isn't mirrored, it's just the text is on the 'inside' of two folded pieces of plastic.
Here's the progression of how the keyboard was assembled:
The back was attached by a dozen or so plastic rivets. This makes the keyboard pretty much un-disassemblable. If it's broken, tough luck.
The broken part of the keyboard. You can already see a few of the traces on the ribbon cable were borked. It's even worse where the ribbon cable attaches to the matrix. I could fix it with glue and conductive ink, but it's seriously not worth my time or trouble.
Finally, keycaps. Yes, doubleshot. I have yet to do the full-on keyboard science to figure out what they're made of, but my guess would be ABS.
I might be getting a few more of these keyboards, so I made a matrix tester:
Just some LEDs and a few resistors. As far as I can tell, this keyboard is pretty much the same asthe Czech keyboard from this project. The matrix seems to be the same, at the very least.