Following are currently work in progress milestones.

Scope determined: April 2008
Beta 1: Late 2008
4.0 Final: 2009

You can follow Flex 4 SDK page for more feature announcements.

Following are top Open Source Frameworks:

1. Cairngorm
   “The Cairngorm micro architecture is intended as a framework for Enterprise RIA developers. If you are writing a very simple application (such as a prototype application) or an application with only a single view, then you might consider a “Model 1″ solution that doesn’t strive for the same separation of model, view, and control that Cairngorm advocates. The benefits of the Cairngorm architecture are realized when developing complex RIA applications with multiple use-cases and views, with a team of developers, and with a multi-disciplinary development team that includes designers as well as creative and technical developers.” by Adobe
   Download Cairngorm.
2. PureMVC
   “PureMVC is a lightweight framework for creating applications in ActionScript 3, based upon the classic Model-View-Controller design meta-pattern.This free, open source framework does not depend on any Flash, Flex or Apollo classes, and is therefore suitable for architecting applications on any platform running AS3.” By PureMVC
   Download PureMVC
3. Model-Glue
   “The Model-Glue family of frameworks support Web application developers by making the construction of Object-Oriented Web and Rich Internet Applications a straightforward process.
   Through a simple implementation of Implicit Invocation and Model-View-Controller, they allow applications to be well organized without sacrificing flexibility.” By Model-Glue
   Download Model-Glue
   
4. Foundry
   
5. Guasax Flex Framework
   
6. ARP
   
7. Flest Framework
   
8. EasyMVC
   
9. Adobe FAST
10. Joeberkovitz’s framework

Here are some Q&A Discussed with James Gosling which are specifically for Adobe Flash / Flex / AIR.

How will JavaFX be positioned with regard to Microsoft Silverlight and Adobe AIR?
[James] : It certainly competes with both of those. I think we have a much broader and more capable API set. We’ve got a much stronger security story and cross-platform story and a really strong performance story. And I think our deliverable will be really nice.

As organizations think about building rich Internet applications or rich client applications, when should developers look at JavaFX over competing technologies?
[James] :Â “If you look at something like Flash, when you get to the much more advanced stuff — richer interfaces, more complex network protocols, more complex APIs — it really falls short.” We’ve had a platform for years that can build rich Internet applications that are extremely sophisticated.
Our issue hasn’t really been, can you build interesting rich Internet applications? But that it’s difficult. And most of our efforts really are around making a lot of it easier.

In RIA technology space Flash Platform and AJAX are leader and Microsoft (Silverlight) and SUN (JavaFX) are just coming in action.

I am sure that Flash/Flex Platform Community will have some reaction on this.

You can read full article here…

Find out more details here…
How to install subclipse in Flex Builder (eclipse).