1). TinyMCE

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 Content Management Systems.

Homepage:http://tinymce.moxiecode.com/
Download: Download TinyMCE 3.1.0.1 stable

2.) FCKeditor

FCKeditor is a full featured, well-documented & simple to use WYSIWYG HTML text editor. It is lightweight, easy to implement.

With an integrated powerful ajax file manager, CKFinder, you can control both the media & content of your web applications.

Homepage:http://www.fckeditor.net/
Download:
FCKeditor_2.6.2.zip
FCKeditor_2.6.2.tar.gz
FCKeditor.Net
FCKeditor.Java

3.) NicEdit

NicEdit is a Lightweight, Cross Platform, Inline Content Editor to allow easy editing of web site content on the fly in the browser.

NicEdit Javascript integrates into any site in seconds to make any element/div editable or convert standard textareas to rich text editing.

Homepage:http://nicedit.com
Download: NicEdit 0.26
Choose the NicEdit Components you Need

4.) openWYSIWYG

openWYSIWYG is a free cross-browser WYSIWYG editor that’s shipped with most of the rich-text editing features you need.
This editor works as a textarea replacement with a single line of code. It can be used with any programming language as it is coded entirely in JavaScript.

Homepage:http://www.openwebware.com/
Download: openWYSIWYG 1.4.7

5.) markItUp

markItUp! is a JavaScript plugin built on the jQuery library. It allows you to turn any textarea into a markup editor. Html, Textile, Wiki Syntax, Markdown, BBcode or even your own Markup system can be easily implemented.

Homepage:http://markitup.jaysalvat.com/
Download: markItUp! pack 1.1.2

6.) obedit

obedit is a Flash-based rich text editor. It will allow a user to edit text much like you would in an office-like application, with simple editing features like bold, italic, justification, block indents, text color, font and size selection, links, bullets, background color, and spell checking.

Homepage:http://www.oblius.com/projects/obedit/
Download: obedit 3.04 beta english (LGPL)
obedit 2.41 english (LGPL)