Lily is a Firefox add-on that allows users to create rich, complex applications in a web browser. With Lily it's possible to make programs that mashup the web or the desktop, visualize and animate data, modify webpages, play music, or connect to world outside the computer.
TinyMCE - Javascript WYSIWYG Editor
TinyMCE is a platform independent web based Javascript HTML WYSIWYG editor control released as Open Source under LGPL by Moxiecode Systems AB. It has the ability to convert HTML TEXTAREA fields or other HTML elements to editor instances. TinyMCE is very easy to integrate into other Content Management Systems.