GPIB

HP originally built the bus as HP-IB (Hewlett-Packard Interface Bus) to connect measurement instruments to its computers, and it became a formal standard as IEEE-488 in 1975. Up to 15 devices shared an 8-bit parallel bus through a chunky 24-pin connector that could be stacked one on another.

HP's own pen plotters accepted HP-GL commands over exactly this bus, and some printers rode along too. Slow by modern standards but robust and addressable, it is still used by laboratory instruments today, often tunnelled through USB or Ethernet rather than the old cable.