Spry is a JavaScript framework for creating Ajax applications, a library that makes it easy to incorporate XML data into HTML pages using HTML, CSS, and JavaScript.
Want to learn more? Paul Gubbay has written an introduction to Spry. Spry examples are posted on Labs. And you can download Spry from Labs.
Builder.com is running a story by Andrew Muller on Flex 2. Andrew gives a great overview of Flex, discusses AJAX, talks about Flex pricing, and more. Recommended reading.
Check out the JBoss Collaboration Server and the Flex based JBoss Mail Client effort.