WYSIWYG editors - are Web Content Management Tools which display word processing icons above a text area that function like the buttons of a word processor. For example, "Bold" will change the text you have selected to become bold. You can add an image to your webpage making editing quick and easy. Such editors are usually highly customizable allowing you the choice of showing or hiding each button as desired.
TinyMCE: Plone 4 Visual Editor
TinyMCE, a platform independent web based Javascript HTML WYSIWYG editor, is a default visual editor in Plone 4. It allows to edit content on Plone websites as easy as in any other text editing software.
The following screencast - is an overview of the TinyMCE visual editor. The basic text editing, including image insertion, is shown here as well as the procedure of customizing TineMCE editor toolbar.
Kupu: Plone 2, Plone 3 Visual Editor
Kupu as a default visual editor for Plone verison 2 and 3. It is currently available for recent browsers (IE >= 5.5, Mozilla >= 1.3.1 for all Operating Systems, Netscape >= 7.1, Firefox >= 1.0 for all Operating Systems) that supports Rich-Text-controls (called Midas for Mozilla).
Kupu uses CSS in favor of HTML for layout and presentation. It supports asynchronous saving to the server. It sets event handlers from code instead of from the HTML (excepting the toolbar), which makes the code a lot cleaner. It uses DOM functionality to build up HTML. On those and other fronts it tries to use the most modern standardized techniques available on all supported browsers to ensure a good user-experience and clean code.
Have a look at our Kupu Screencast to see this widely used Plone WYSIWYG editor in action.