The never-released HP-72S / HP-74S - the successors of the HP-71B

[sa-penguin]

If there was an "in line" USB module, that had an LCD...
And sat between a standard keyboard and a PC...
And could be invoked using a "Hot" key combination...
...that could be used as a calculator.

Don't even need a PC, either - a USB power supply would be enough.

Of course, someone would put a 2nd USB port on it, throw a memory stick on it, and use it to edit files. Or encrypt / decrypt data without exposing the key to the PC.

People can be very inventive.