From the website:

Making Ajax and Related Technologies Accessible

Many Web applications developed with Ajax, DHTML, and other technologies pose accessibility challenges. For example, if the content of a Web page changes in response to user actions, that new content may not be available to some people, such as people who are blind or people with cognitive disabilities who use a screen reader.

Web sites are increasingly using more advanced and complex user interface controls, such as tree controls for Web site navigation. To provide an accessible user experience to people with disabilities, assistive technologies need to be able to interact with these controls. However, the information that the assistive technologies need is not available with most current Web technologies.

WAI-ARIA addresses these accessibility challenges by defining how information about these features can be provided to assistive technology. More specifically, ARIA provides a framework for adding attributes to identify features for user interaction, how they relate to each other, and their current state. With ARIA, an advanced Web application can be made accessible and usable to people with disabilities.

 

From the website:

Fluid is a worldwide collaborative project to help improve the usability and accessibility of community open source projects with a focus on academic software for universities.  We are developing and will freely distribute a library of sharable customizable user interfaces designed to improve the user experience of web applications.

This could be a helpful org for penntags 

Very nice and informative FAQ on testing webpages in screen readers.  Note the 2nd from last question in this FAQ.