Including the Unix shell line editor, which typically supports both vi and emacs key bindings, and nothing else. Yet for some reason the default always seems to be emacs rather than vi, even on BSD (e.g. OpenBSD), and even though POSIX only mandates vi mode because "[t]he author of emacs requested that the POSIX emacs mode either be deleted or have a significant number of unspecified conditions."[1] Emacs line editing mode is more confusing for me as I use Joe (WordStar clone) which has emacs-like key combinations but with slightly different assignments. And because of this default I've never made a habit of using line editing commands; there's no way I can unlearn my Joe muscle memory, and over the years I've gotten into the habit of avoiding shell personalizations, to my detriment in this case.
[1] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/s...