CKEditor : CKEditor is an open source WYSIWYG text editor designed to bring common word processor features directly to web pages, simplifying their content creat...
Strut : An HTML5 Presentation Editor. A GUI / Authoring Tool for ImpressJS and Bespoke.js
Source at https://github.com/tantaman/Strut
mmm.page : Dead simple, drag & drop personal websites.
NicEdit : WYSIWYG Content Editor, Inline Rich Text Application
Slate : Slate is a completely customizable framework for building rich text editors.
Slate lets you build rich, intuitive editors like those in Medium, Dropbo...
an open source rich text editor based on HTML5 technology and the progressive-enhancement approach.