What is something that's crazier than the wildest dreams of any ~1970s nerd, but exists today? I'll start with an easy one:

Blue LEDs. We had red and green since the '60s, but blue took until the '90s to figure out and the guy who did so got a Nobel prize for it because that finally meant we could use them for white lights and full-color displays.

I remember when the only color laser pointer was red. Now you have all the colors of the rainbow.