The Turbografx 16 (or Turbografx PC-Engine in Japan) has the most amazing fucking expansion port I've ever seen. Every bus is exposed, plus sound out and IN (unused by anything ever made for the thing), composite out (not included on the console itself, but 3rd-party addons allowed it), VGA out (!!!) and CPU HALTING/CLOCK CONTROL were included over this fucking thing.

You can even power the system with 5v in through the expansion port and bypass the power switch with it.

Info and diagram:
https://gamesx.com/misctech/...

Example:
To get composite out, send pin A22 out and ground the ground wire of the composite to any ground.
For VGA, it's a little more complex:
VGA1 to TG-A23, VGA2 to TG-B23, VGA3 to TG-C23, VGA9 to TG-A2, VGA13 (and VGA10 if you want compatibility with older displays) to TG-B11, VGA14 to TG-A10, VGA5-8 (and 10 if not hooked to TG-B11) to TG-C2
(VGA numbering from Wikipedia diagram)

this thing's fucking cool