Mercury is a full featured HTML5 editor

Mercury Editor is a fully featured editor much like TinyMCE or CKEditor, but with a different usage paradigm. It expects that an entire page is something that can be editable, and allows different types of editable regions to be specified. It displays a single toolbar for every region on the page, and uses the HTML5 contentEditable features on block elements, instead of iframes, which allows for CSS to be applied in ways that many other editors can’t handle.

http://jejacks0n.github.com/mercury/