Let's say you're interested in UFOs. It's a fun hobby, but you'd like to monetize your efforts. What do you do?
Historically, your avenues were limited. There was entertainment—science fiction movies like Close Encounters of the Third Kind (1977) or E.T. (1982), purportedly nonfiction books like Chariots of the Gods? (1968) or The Mothman Prophecies (1975). There was journalism, sometimes serious but mostly sensationalist. There were conferences and festivals where you could make money with attendance fees and UFO-themed merchandise.
