This has been rolled into the latest release (2.3.0) of the YUI Library
You can see it here: http://developer.yahoo.com/yui/editor/
This is a prototype Rich Text Editor built with the YUI libraries.
Most of the features work in IE, Firefox, Opera & even Safari (Currently firefox works best).
Known issues with IE: Can't change the font family and font color, the toolbar flickers when you change something.