NicEdit!

TinyMCE is a platform independent web based Javascript HTML WYSIWYG editor control released as Open Source under LGPL by Moxiecode Systems AB. It has the ability to convert HTML TEXTAREA fields or other HTML elements to editor instances. TinyMCE is very easy to integrate into other CMS systems.

CKEditor is an open source WYSIWYG rich text editor and collaboration solution designed to bring common word processor features directly to web pages, simplifying their content creation.

A lightweight WYSIWYG BBCode & HTML editor

CLEditor is an open source jQuery plugin which provides a lightweight, full featured, cross browser, extensible, WYSIWYG HTML editor that can be easily added into any web site.

Aloha Editor is an HTML5 WYSIWYG Editor that gives you a total new experience when editing. It's faster than existing WYSIWYG technologies and offers unprecedented WYSIWYG functionalities.

WYMeditor is a web-based WYSIWYM (What You See Is What You Mean) XHTML editor (not WYSIWYG).

Introduction

A full-featured open-source web site-creation package designed for the academic community.A single OpenScholar installation can host thousands of personal or project sites.

Redactor Text Editor is a WYSIWYG html editor.Redactor provides smooth and clean design, limitless flexibility and extensibility, simple and super-efficient API and amazing user experience.

MediumEditor is a Medium.com WYSIWYG editor clone, a dead simple inline editor toolbar. Uses contenteditable API to implement a rich text solution.

Finally, a free open source cross-browser WYSIWYG editor thats packed with every rich-text editing feature you need.