It's kinda stuff like this that makes me wonder what things are considered useless right now that will be the most important invention in the future
French mathematician Pierre de Fermat wrote a "little theorem" in 1640 that is now the basis of modern computer cryptography.
The Fast Inverse Square Root is an algorithm that estimates 1/sqrt(x), a very important calculation in computer graphics. Early computers struggled when calculating this value but a programmer solved this mathematical problem...while programming Quake 3. His solution to the problem wasn't discovered until the source code for the game was released.
The Greeks actually also invented steam engines. But they didn't know what to do with them. So instead it was just a fancy art piece that spins super fast.
They also invented a lot of other stuff: door bells that sound like birds chirping, automatic doors, clocks which tracked the year, etc.
