Shimano Dura-Ace indexed rear gear
Indexed gearing started long before Shimano produced their very well behaved Shimano Indexed Shifting (SIS) system. The first that Hilary notes is the Super Champion Osgear from the 1930's. Shimano's first indexed derailleur was the Positron, which was a low level derailleur with the indexing occuring at the derailleur itself. Improvements in the shape of the rear cogs, cable housing, and the incorporation of slant parallelograms in derailleurs were among the factors that made the Shimano system so well behaved and therefore so successful in the marketplace.
Steve in Peoria