EpicEditor seems to just keep growing. It's been on HN's front page a few times. There's a version for just about every environment from Node, Ruby, to Python to every CMS such as WordPress, ExpressionEngine and more. It's even been placed in an Adobe Enterprise on-prem app. I honestly can't keep up which is a shame because I think it can grow into something even greater with a little TLC :)
If you or someone you know has worked with HTML WYSIWYG type open source projects (contenteditable APIs, etc) comment in the GitHub ticket I just made (copy pasted most of this message), or you can email me at oscargodson@outlook.com.