One might point out that this is the story of AI since at least the 1930's. Impressive technology demo's ... wild investment, crash, bankruptcy ... but the tech remains and in fact has useful applications all around.
AI Winters. I finished school in 2008 and have seen it happen twice.
Vocoders, (voice encoder-decoder, they effectively compress voice) which were going to enable computers (the analog kind) to respond to human speech in callcenters (because editing/generating the compressed stream is hard, but actually doable)
Of course it was a joke.
But ... it was used. What they were used for a little bit is voice encryption, in military communication. Vocoder -> encrypt -> transmit -> decrypt -> Vocoder and you can "talk", if you don't mind the extreme voice distortion.
Oh and the talking clock on the telephone network. That, they got working.
AI Winters. I finished school in 2008 and have seen it happen twice.
Convnets. LSTM (and various RNNs).
Both are in wide use today.