Solid body electric guitars- the first models have been in continuous production and are still available.

https://en.wikipedia.org/wiki/Fender_Telecaster

https://en.wikipedia.org/wiki/Gibson_Les_Paul

There were earlier "electric guitars" but I'm thinking all inventions build on previous creations. I don't think you'll find many pure answers to OPs question. I think the closest you'll find is going to be an advancement that produced a single step change in design that flattened the innovation curve forever after. I think the microwave oven was a great example.

Electric fuses also come to mind. Little has changed since 1890.