Kind of like the mystery airships that were plaguing us at the end of the 19th century? But I think the OP was talking more about normal, mortal, earthbound hu

Kind of like the mystery airships that were plaguing us at the end of the 19th century? But I think the OP was talking more about normal, mortal, earthbound humans having some garage-built technology that got classified as UFOs. Those would necessarily have to be made with the technology of the day.