Amstrad joystick splitter
With the old Amstrad CPC computers you could connect 2 Amstrad joysticks to the computer by connecting the second joystick to the port on the first (there was only one port on the computer itself). This was fine if you had an Amstrad joystick.
If you happened to have non Amstrad joysticks (Kingston, Quickshot or Atart etc.) you were limited to one.
Below is a wiring diagram showing how to make a cable that allows you to connect two joysticks to the single port on the computer.