The Disco Ball
It's older than the light bulb's mass adoption, patented under a name nobody uses, and it wasn't built for dancing at all.
Long before disco existed, a group of electricians in Charlestown, Massachusetts wanted their 1897 annual union party to be seen from across the city. They rigged up lamps and an arc light, bounced the glow off a cluster of small mirrors on a sphere, and reported the effect could be spotted for miles.
Nobody patented that party trick. It took another twenty years for inventor Louis Bernard Woeste, working out of Newport, Kentucky, to file the first real patent in 1917 for what he formally named the 'Myriad Reflector,' designed to scatter moving, varied color spots across a room. The application makes no mention of dancing or music at all.
Disco itself wouldn't exist as a genre for another five decades. By the time the mirror ball became inseparable from the 1970s dance floor, Woeste's original name had vanished so completely that even historians researching the object only find it by accident, buried in early-1900s patent filings for something nobody had yet thought to call a disco ball.
The disco ball was not invented for disco -- it existed as a lighting novelty at least five decades before the genre it's now synonymous with even existed.