Hang Glider: A simple frame and fabric glider with the pilot suspended in a harness so that the aircraft can be guided by shifting the pilot’s weight. Nowadays, hang gliders are made from aluminum tubing and nylon. Beginner flights are short and close to the ground, but experienced pilots can soar for hours. HangGliding.org
Tech Level: Low. Could be made from wood and sailcloth, so Age of Sail. Could be made of bamboo and silk, so good potential in the Tang Dynasty. Conceivably, since metal is not a requirement, Stonepunk. Wonderful for Time Travel or Alternative History.
Appeared In: Windhaven, by George R.R. Martin and Lisa Tuttle. A favourite of mine. In this book, the flyers have collapsible wings constructed of materials salvaged from their ancestors’ space ship. Avatar: The Last Airbender, an animated series I admire for its complex characters, also featured a folding glider.
For Your Plot: Anything goes! The hang glider rivals the hot air balloon for any character that needs to go flying in a low-tech environment.
Hovercraft: A machine that uses powerful fans to float on a cushion of air. As a teenager, I crossed the English Channel in one. It was quick, but expensive. And noisy. With a ride height of a meter or more, they should have great potential for travelling over ice, water or desert terrain. Military ones were used in Viet Nam, where they provided splendid mobility in river deltas. Since then, both military and civil applications seem to have fallen into decline without ever really taking off.
Tech Level: High. Light powerful engines are a must. Probably most at home in SF or Military SF, where they can be used to travel alien landscapes. Might be good in climate-themed post-apocalypse tales.
Appeared In: Nope. Drawing a blank here.
For Your Plot: When global warming floods Manhattan and the starving stockbrokers turn all Waterworld on you, you could skim over the treetops of Central Park in your hovercraft. You’d be quick, but not stealthy. Watch out for currency traders on jet skis. Expect to hit stuff, hovercraft are notoriously hard to steer.