Slightly OT, but there was a standalone software just like gingko for the Mac. Do you now something about it?
Edit: I think it was an old version of gingko as a desktop app. Still available at https://github.com/gingko/client/releases
Edit: I think it was an old version of gingko as a desktop app. Still available at https://github.com/gingko/client/releases
https://www.hogbaysoftware.com/bike/
(Maybe not — this isn’t markdown first; but it is a very macOS-y, keyboard driven, hierarchical outliner that I enjoy.)