NOTE: This is not a list of "one-hit wonders" who directed more than one film; this is a list of one-and-dones.
These are these directors' only features. Many of them make me weep for their creators' not being able to follow up.
There's a lot of actors/writers/etc in here, realizing directing is hard & walking away after one, but there's also careers that were simply cut short, which sucks just as bad.
(Note: Not all once-only films are amazing, or even worth watching; I'm omitting a lot of schlocky horror films & bad sexploitation joints from here, especially (for some reason) Italian ones. And I'm alphabetizing this list instead of putting them in rating order, because people are looking for their fave, which I totally get. If it's not here, let me know.)