Eprom emulator .. the idea was to make an eprom emulator that was easy to make. So most of the wiring and pulldown resistors are one module and only the signals that are needed are fed trough a connector, so the electronics could be easily developed on a breadboard.
Test pen .. this pen used to be a light pen which i made for the C64 but i changed it later in a testpen. It is usually connected to a small microcontroller like the SX. It has a pin to make contact which is thin enough not to shortout IC pins, the microswitch is used in functions in the controller, like resetting flip flops, give short pulses, switching programs.