Demo on a Comodore 64 with probably one of the weirdest visualizations/music players I've ever seen.Playing music on an IBM 1401 mainframe. Interestingly, the IBM 1401 had no speakers, no sound card, and no physical way of actually playing music normally. What's happening is that in an era before the FCC had decent regulations on radio wave emissions, the IBM 1401 would emit fairly powerful radio signals and by running certain instructions on the processor you could basically use the processor as a transmitter and generate a modulated wave that would play music on a nearby radio tuned to the right frequency.
You can actually do the same thing with a Raspberry Pi today, except using a clock signal on one of the GPIO pins instead of the processor itself. It just spits out frequency modulated signals right on 100 MHz, so the Raspberry Pi will happily transmit right over commercial radio.
TRS-80 playing background music for Frogger. Not especially amazing either until you learn that the TRS 80 also had no way of playing music itself, and instead programs just had to dump square waves on the cassette port to generate tones and hope someone plugged some speakers in.
You should be able to do the same thing with your favorite TI graphing calculator on the IO port.
Default song on a tracker for the ZX Spectrum.
