The PC game port is a nearest thing to intentional GPIO that PC has. Parallel port is almost always better for digital GPIOs, but it was not designed that way and the fact that it can be used like that (and extended several times into what in the end was SCSI-like protocol) is kind of an coincidence.
> The PC game port is a nearest thing to intentional GPIO that PC has.
Er, what? Not every IBM PC (clone) had a (sound) card with joystick ports, but almost every PC clone had (ISA, later PCI) extension slots. There were/are plenty of digital i/o adapter cards for those available, from plain, cheap 8255 based ones to those with slave CPUs (potentially more powerful than the host's CPU).
But then, perhaps I don't understand what you mean by 'intentional' GPIO.
