Certain implementations of the GPIB bus, also known as IEEE-488 bus and HPIB bus, were not capable of arbitrating between multiple bus masters. This was a problem if you wished to share a set of resources, such as printers and plotters, over a set of computers.
During my sixth form studies at Richard Taunton College, we built a number of GPIB Combiners to my design. These allowed multiple IEEE-488 bus masters to share a single set of peripherals. Therefore, the Commodore printers and floppy-disk units became fileservers for a number of PET computers.
The design was finally published in Wireless World in April 1984 and various commercial companies started making these devices.
Unforunately I can't find any photos of any of the prototypes, but here is a view of the Computer Club of 81, with some of the equipment visible left, including our Kode Teletype, the paper tape winder, the monitor for an 80x24 terminal and the SWTC 6800 system (South West Technical Products). I also built a GPIB interface for the SWTC machine, so it too could share the peripherals.