The microwave oven, aka the "Popcorn and Hot Pockets Warmer," was a happy accident that came from, of all things, a weapons program.
Percy LeBaron Spencer was a self-educated engineer working on radar technology in the years following WWII. The technology in question was the sci-fi sounding magnetron, a piece of machinery capable of firing high intensity beams of radiation.
Above: a scientist, with robot.
Apparently, P.L.S., as some have called him, had a bit of a sweet tooth. Or a strange fetish. Either way, he had a candy bar in his pants while he was in the lab one day. The self-proclaimed engineer noticed that the chocolate bar had melted when he was working with the magnetron.
Spencer disregarded the simple idea that his body heat had melted the chocolate in favor of the less logical and therefore more scientific conclusion that invisible rays of radiation had "cooked it" somehow.
A sane man would stop at this point and realize these magical heat rays were landing just inches from his tender scrotum. Indeed, most of the military experts on hand probably dreamed of the battlefield applications of their new Dick-Melting Ray. But like all men of science, Spencer was fascinated and treated his discovery like a novelty. He used it to make eggs explode and pop kernels of corn ("Imagine, a future where a building full of workers in cubicles eat this all day!")
I proclaim myself to be awesome.
Spencer continued to experiment with the magnetron until he boxed it in and marketed it as a new way to cook food. The initial version of the microwave was roughly six feet tall, weighed in around 750 pounds and had to be cooled with water. But they got it down to size, and today we use it mostly to destroy random objects on YouTube.
Krazy Glue and/or Super Glue
The story goes that in 1942, Dr. Harry Coover was working for Eastman Kodak, a company renowned for cameras and camera-related things. His job was to find a plastic that could be used as a clear gunsight, since this was smack in the middle of WWII and everybody knew where the money was.
Coover got frustrated because the material, called cyanoacrylate, was just too damned sticky. Rather than noticing he accidentally made one of the most versatile adhesives of all time, he threw it away in a huff and continued sweating over gunsights for a war that would be ended, ironically, by two bombs with blast radiuses so big that they didn't even require sights at all.
Years later, Coover would re-discover his invention, we prefer to think due to him noticing that old container of cyanoacrylate was still stuck to the bottom of his trash can and couldn't be removed by any means.
In 1958, after finally convincing his bosses that at the very least, there was enormous comedic potential in the prospect of a man getting his hand permanently stuck to his junk; Kodak released the glue with the catchy name "Eastman 910."