Covox Speech Thing / Disney Sound Source (1986)
The Disney Sound Source grabs an idea that is pretty simple and easy to achive.
The parallel port is nothing more than a possibility to pass out 8 bits simultaneously. Each PC had this port, and the conversion of this kind of data to electric oscillations represented only a small, very uncomplicated step. Hence the only thing missing was the interface, which a company named Covox delivered with their "Speech Thing". For $70.
However, this utensil was nothing further than soldering together some different resistors, the simplest form of a DAC at all, and actually was not worth its money. However, its simplicity allow it to build it at home (see link).
Some other versions even supported the recording (!), and there are even circuits, which made stereo playback possible using a switching circuit with two DAC's.
A quite similar product was sold by Disney, named "Disney Sound Source". This one was built technically somewhat more complex in order to allow to use a printer without changing the plugs. Using a 9V battery, it even featured an integrated amplifier!
There are only few games, that supported the parallel port as sound possibility - whether now using Covox or Disney Sound Source. However, the Covox playback was later quite wide spreaded in the demo scene.