I keep hacking on my Markdown-based text editors at https://saturn9.studio/

I went on a side quest to strip out ProseMirror and markdown-it and implement a custom stack instead. I open sourced both the parser and editor (https://saturn9.studio/technology/):

* Markoffset is a fast, plugin-based, incremental Markdown parser: https://github.com/saturn9studio/markoffset

* Scribeframe is a text editor engine: https://github.com/saturn9studio/scribeframe