By greatest invention I mean something that had big and positive influence.
3D printers were a 21st century invention, I think.
Quadcopters and other multirotor designs resulted in an incredible leap in affordable cinematography, racing applications, rescue, mapping, and warfare.
A lot of 3D printing patents from the 80s and 90s expired between 2010-2020, clearing the way for commercial 3d printers and a million innovations. I’d call them honorary 21st century inventions, since the patent holders squandered the technology in the 90s.
https://www.finnegan.com/en/insights/articles/how-patents-die-expiring-3d-printing-patents.html
We had a 3d printer in the 90s at my Uni. It built layers with laser cut paper lol. It was the cheapest version available and it lived in the engineering department for rapid prototyping. This link says they were invented in 1981, metal sintering was added in 1988 and fused filament in 1989. https://ultimaker.com/learn/the-complete-history-of-3d-printing
