The medium-editor project is pretty good. It's not a "true" clone of the medium editor, but it gets development up and going pretty quickly with a contentEditable editor. We used medium-editor for http://www.doctant.com.
As others have noted, it's really tough to compete with text editing/rich text applications (e.g., Sublime, Vim, Word, etc.) on the web. So far, the real Medium is the only app that I've used that isn't a pain to write in even though it's contentEditable.
As others have noted, it's really tough to compete with text editing/rich text applications (e.g., Sublime, Vim, Word, etc.) on the web. So far, the real Medium is the only app that I've used that isn't a pain to write in even though it's contentEditable.
Another promising project is draftjs from Facebook. Check it out: https://facebook.github.io/draft-js/.