1715IO. Company Rockwell bought 7 or so years ago, most for their redundant IO, which 1756 is **** at. Not sure if you can use them in a safety app, guardlogix, that would be a requirement for me
I very much doubt someone buys a company focusing on triple redundancy processor based systems because of redundant IO.
This was Rockwell aiming at high value safety applications, particularly in process industries (just as their investment in PlantPAX started taking shape).
There's also a not negligible amount of these things (processors and IO) operating in the bottom of the ocean all around the world too.