[slantyyz]

OP looks like it's based on Prosemirror:

"A React and Prosemirror based editor that powers Outline.."

FWIW: I was researching editors that supported live Markdown shortcuts (similar to Dropbox Paper) a while back, and found these alternatives to ProseMirror:

HyperMD: https://laobubu.net/HyperMD -- based on CodeMirror

Quill Markdown Shortcuts: https://github.com/patleeman/quill-markdown-shortcuts - plugin for Quill.js

Both have their pluses and minuses. I found HyperMD to be too heavy and opted for Quill + Quill Markdown Shortcuts for my project.