https://en.wikipedia.org/wiki/Ram_air_turbine
And besides that, there is the looping parachute APU.
https://patents.google.com/patent/US9452721B2/en
Would imagine these are significantly more useful on heavier and faster aircraft - surely the weight and whatnot to retract move them is less worth it for smaller planes ?
And besides that, there is the looping parachute APU.
https://patents.google.com/patent/US9452721B2/en