Latest Web application development Technologies
You have mixed it all up. You have two layers here : user interface which makes the app "rich", and server-side code.
Works best with .NET platform. I wouldn't consider to join it with Java, Ruby on Rails, PHP or something.
Tools are commercial.
Flash/Flex (Flash Platform)
My favorite and I think the most mature one from the list (I's my subjective opinion as I work as Flex/Java developer). Works with all server side technologies using simple Http service, WebService byt the best integration is by AMF services (efficent binary protocol). Integration is on different levels. Basic remote calls (it's enough for 90% projects) are availibe for all platforms (.NET, Java EE, PHP, RoR). but there are library for hi-level interation (data synchronization, data push, client-server events or even client-server depndency injection) for Java EE : Adobe Livecycle Data Services (commercial) or GraniteDS and Tide Framework (free, works wich JBoss Seam).
Flex SDK (compiler and lib) is free, but FlexBuilder is commercial.
SDK is free, IDE is rather poor.
JavaFX / Java Applet
It's rather experimental, graphical tools and IDE are poor. the idea is to declaratively (but not XML) code swing interface and run it as applet. I think id doesn't have production status.
Flash/Flex and Silverlight gives you the most advanced tools to create rich user experience interface with multimedia (video/audio streaming, usage of webcam, microphone etc).