Quill - Your powerful, rich text editor
quilljs.com/Quill is a free, open source WYSIWYG editor built for the modern web. With its modular architecture and expressive API, it is completely customizable to fit any need.
StackEdit – In-browser markdown editor
stackedit.io/Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.