A simple open source platform in Java supporting add-ins.
Add-ins for text, and for syntax highlighting sourcecode are provided.
Aesop is a fledgling Eclipse wannabe looking for add-in developers.
Aesop makes use of JEditTextArea and JavaHelp.
ZWebEdit is a Java applet that is designed to replace the <textarea> tag with a rich Java text editor designed for editing HTML / code in a browser. ZWebEdit does not create a its own filesystem; it is designed to work with Zope or standalone.