CKEditor : CKEditor is an open source WYSIWYG text editor designed to bring common word processor features directly to web pages, simplifying their content creat...
mmm.page : Dead simple, drag & drop personal websites.
Strut : An HTML5 Presentation Editor. A GUI / Authoring Tool for ImpressJS and Bespoke.js
Source at https://github.com/tantaman/Strut
NicEdit : WYSIWYG Content Editor, Inline Rich Text Application
Xinha : Xinha is a powerful WYSIWYG HTML editor component that works in all current browsers. Its configurabilty and extensibility make it easy to build just ...
an open source rich text editor based on HTML5 technology and the progressive-enhancement approach.