As a car enthusiast, I can think of a good one, the Ford Nucleon.
During the 1950s and 1960s, there was considerable interest in nuclear power and its potential applications. This led to the idea of using nuclear energy to propel cars. The concept behind a nuclear car was to utilize a small nuclear reactor to generate steam, which would then power the vehicle’s engine.
Of course back in those days, this was extremely futurustic and some at the time thought this would be a game changer, but ultimately, the safety aspect was one of the biggest reasons why this idea was dropped, and I probably don’t have to explain why it may not have considered to be safe, I mean, it was using nuclear power, so even if the engineers tried to make it as safe as possible, IF something went wrong, it would have been catastrophic.
Ever since then, the interests in the automotive sector has shifted to Electric and Hydrogen.
Still, a very intriguing concept car and idea.
Outside cars, you have blimps, and I personally believe if we tried to make something like a hindenburg today with existing technology, we might have been a lot more successful than back then (as it goes way back to 1930s), there are still some blimps used occasionally, I also don’t believe those use hydrogen(?), but they are not the “game changer in air travel” it was once seen as, although we can’t rule out a comeback.
What about you guys?
DCC, Digital Compact Cassette. It was introduced by Phillips in 1992 and was supposed to be the successor to the old music cassette. It was digital, with sound quality comparable to a CD, but the players were also compatible with the old cassettes. In theory this was a great idea but it never went anywhere, and the format was discontinued on 1996. I think Techmoan has a video on it.
Reminds me a lot of Laserdiscs, which were digital (kinda, the media was digital but stored and read manually, making it technically analog) media discs, basically like a 12" vinyl, made to replace VHS tapes. Their only relevance in the past two decades has been a single episode of Regular Show
IIRC Laserdisc actually was the best quality home video format for a while, and it had a nice content library. Wasn’t it quite popular in Japan? DCC never went much anywhere. Its main competitor, MiniDisc, had some niche appeal for portable players, but once mp3 players took off it too was finished.