Kupu is an open source editor for Firefox, Netscape and Internet Explorer. It is one of the most widely used WYSIWYG editor among Plone-users. Kupu was written by Paul Everitt, Guido Wesdorp and Philipp von Weitershausen to improve the JavaScript code and architecture, standards support, support for webservers other than Zope, customization, and other issues.
The following is a list of screencasts about Kupu visual editor: