The Rich Text Editor is an easy-to-use editor that can be added to any project that might need user input. It offers a couple of versions so you can decide where on the cost (bandwidth)/benefit (features) curve you want to be.
The RTE is also highly customizable and we've seen how to add tools to its toolbar and their associated actions, and how to customize the looks of the editor window.
Its rich set of events plus the dynamic events let you add code to capture everything that happens in the RTE and respond accordingly.
The flexibility of the RTE is reflected in the home page for the component at the YUI site, where the list of examples shows the many ways in which it can be improved or tailored for specific needs.