TOAST UI Editor
Markdown WYSIWYG Editor. GFM Standard + Chart & UML Extensible
... Editor follows both CommonMark and GFM specifications. Write documents with ease using productive tools provided by TOAST UI Editor and you can easily open the produced document wherever the specifications are supported. Through the context menu of the table, you can add or delete columns or rows of the table, and you can also arrange text in cells. Highlight the code block area corresponding to the language provided by Prism.js.