wysihtml5

wysihtml5 is an open source rich text editor based on HTML5 technology and the progressive-enhancement approach. It uses a sophisticated security concept and aims to generate fully valid HTML5 markup by preventing unmaintainable tag soups and inline styles. The code is completely library agnostic: No jQuery, Prototype or similar is required.

html5wysiwygtextareaeditor

http://xing.github.com/wysihtml5/