⚙️Lost / Stolen & Hidden Turn of the 20th Century Inventions

Just the tippy-tip-top of the proverbial iceberg!
A few minor examples, save for the "anti-gravity" flying platform vehicle.
Yeah, it's real, but Sacha Stone says it doesn't repel gravity, more utilizing the electromagnetic field. IDK!
WHEN THE WHOLE WORLD WAS ON COURSE FOR GREATNESS!