Adobe's client-side (RIA) technology, Flex, is officially matched on the Java server-side by their Adobe LiveCycle product, but it is possible to use different software on the server-side. Here are three options:

The first is an old report: Midnight Coders (now a GlassFish Partner) has official GlassFish Server support in their WebORB for java product, see TA entry. A second possibility is GraniteDS, which currently has Experimental GF Support. The third is Adobe's own open source offering: BlazeDS. Successful reports include Ries at BMK LLC, Igor Costa and Sean. Also see Ryan's comments in this TA post. The most complete series is by Anachronymous: Intro, Choosing GF (over JBoss), and then Part I and Part II.

Mark at The Midnight Coders reports that the latest WebORB is now Fully Supported on GlassFish. WebORB supports multiple RIA clients, including Flex, Flash, Silverlight and AJAX. Check out the the Overview to WebORB, the Java Overview (webORB also supports .Net, PHP, Ruby and ColdFusion) and the Installation page.

Adobe Flex is one of the new Rich Internet Application (RIA) platforms. Two Back-Ends for Flex are Adobe BlazeDS and Midnight Coders' WebORB and Ries reports success in using GlassFish with both: Flex and Blaze-DS and Flex and WebORB. The BlazeDS Release Notes only mention Apache Tomcat, so I'd be interested in additional feedback on whether everything works. If not, since OpenDS is an OpenSource project, there might be some GAP opportunities for some person with energy and expertise. WebORB seems designed for portability from the beginning. Although GF is not listed explicitly in their Container List Reis' has a see Live Demo running on GF (see NetCraft Report).

Metro, the Web services stack in GlassFish, allows you to build secure, reliable, transactional, and interoperable Web services. NetBeans IDE provides an easy way to generate Web service client artifacts and invoke the endpoint from Java classes or pages. The beauty of Web services is that the client and server may be completely disconnected, for example, even using different language. James Ward showed how to use Flex to create a front end to JAX-WS, a core component of Metro.

Let us know if you have used JavaFX or any other similar technology to create a front end for Metro.