I wrote my own editor, many years ago. I have been using it every day ever since, for all the coding work I do. It is a terminal program, so maintenance has not been burdensome.
https://www.github.com/marssaxman/ozette/
If I did it over again, I might use a rope instead of a line array as the central data structure, but it works well enough that I've never bothered to change it.