There is also Joplin (https://joplinapp.org/ https://joplinapp.org/), which is open source and has multiple Apps available (including mobile). I don’t think it

There is also Joplin (https://joplinapp.org/ https://joplinapp.org/), which is open source and has multiple Apps available (including mobile). I don’t think it uses plain markdown files as the primary data store, but notes are written in it and they can be exported as Markdown files.