Carousel Projector (1961 - 2004)
Kodak

Kodak Carousel 1050

Based around the 80 slide carousel, containing 35mm transparencies mounted in a plastic frame.
The only solution to affordable scenic projection until digital projection rendered it obsolete.
The Carousel was used heavily, both in education and in entertainment.
The lower-end projectors had limited control (forward / back through the slides). However, higher-specification projectors had a multipin connector on the back, which provided remote control of those functions as well as a connection to fade in/out the projector lamp.
Using audio pulses on a tape soundtrack, multiple projectors could be synchronised to perform hugely complex sequences.
Early multimedia shows such as Robert Ornbo's I and Albert, Mike Batt's The Hunting of the Snark in 1991 and The Who's Tommy in 1996 relied on the technology.

Models (list under construction)