MODx is a content management system with AJAX goodness (or Web 2.0 as they say). The code is neat and gives a true CMS feel. Though I liked the admin Interface more, the panel offers a wide range of options , Tools, extra plugins , stats checking etc. like a true CMS .

MODx is the first free PHP CMS to offer an API that fully supports Web 2.0 Ajax technology thanks to script.aculo.us. Expect to see this grow more and more into our manager over time, but you can make use of it today in your own custom applications including live search, web effects, Ajax communications and more.

PHP Application Framework – a flexible API and a event model that allows to override how the core behaves means that you get both tremendous flexibility, but also the ability to customize the solution to your needs and a simple upgrade path.

consider MODx your #1 free Search Engine Optimization CMS. MODx helps your SEO efforts by making it easier to adjust meta-content of your site on a per-page basis.

I should say it does a lot more than other AJAX based scripts like AJAXpress and AJAX Portal . But still it needs a lot more to get into high level category of scripts like Joomla and Wordpress.