google html.editor browser.based open source
http://epoz.sourceforge.net/index.html Epoz is an in-browser WYSIWYG editor written by Maik Jablonski. Zope 'document-centric' open source client-side editor for Mozilla, Netscape and Internet Explorer.
http://dmoz.org/Computers/Software/Internet/Authoring/HTML/WYSIWYG_Editors/