Google’s got an editor, an AJAX, WYSIWYG editor. Google Pages.
From the Site:

Google Page Creator is a free online tool that makes it easy for anyone to create and publish useful, attractive web pages in just minutes.
No technical knowledge required.
Build high-quality web pages without having to learn HTML or […]

From the site (http://www.metz.se/tinyajax/index.php):

TinyAjax allows you to:
AJAX enable your pages without having to write a single line of javascript
Call PHP functions in classes or as separate functions, you can even extend TinyAjax by subclassing it
Let your PHP-code set which elements to alter and with what using behaviours
Integrate it with a template system (smarty-example included)
Easily have […]

Users are more advanced and expect more from applications. Simple UI is not acceptable in the 21st century. See this article for more information. It’s quite good; the author dives deepter in to:
The HTTP ready state

The HTTP status code

The types of requests that you can make
Enjoy!

Yahoo! has released an AJAX UI library and a set of Design Patterns. Here you can learn more about Yahoo! UI Lbrary ; and here you can learn more about Yahoo! Patterns.
“The Yahoo! User Interface Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications […]

A really interesting feature of open source is the ability to move quickly in response to user demands. According to this post, PHP will include the php-json module with standard distribution.