Shimano Biopace.

It did not fail due to the engineering or design being bad or the end products lack of quality, it was a marketing failure when Shimano decided to offer this from top to bottom from instead if letting it trickle down from the higher component groups as they have done with everything else.

When you market a product to leisure cyclists and racers at the same time, someone isn't gonna buy it.

There are modern counterparts to these that are getting used successfully at competitive levels.

Shimano also brought us Selecta cranks, a Front Freewheel system, and Positron derailleurs which have not had the same appreciation as Biopace does now as it is appreciated by a fair number of cyclists.

Campagnolo brought us the Valentino groupo... I think they learned to stay out of the consumer market after this.