About a month ago, the Flex team announced that nightly builds of the next version of Flex (code named Gumbo) were now available on the opensource Flex site. Along with early versions of the SDK, the team also posted a ton of other information, including specs and API docs.
Below is a listing of links and resources about Gumbo / Flex 4. Going through these will quickly get your up to speed on what is being worked on in Flex 4, and get your ready for playing around with the new builds.
Official opensource project page
http://opensource.adobe.com/wiki/display/flexsdk/Gumbo
Flex 4 Downloads
http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4
Gumbo Themes
http://opensource.adobe.com/wiki/display/flexsdk/Gumbo+Themes
An Introduction to the Gumbo Component Architecture
http://opensource.adobe.com/wiki/display/flexsdk/Gumbo+Component+Architecture
Flex 4 Language / API Reference
http://livedocs.adobe.com/flex/gumbo/langref/
Videos
The Next Dimension of Rich Experiences (360 Flex Keynote) Mark Anders
http://link.brightcove.com/services/link/bcpid1753161885/bctid1741161343
Flex SDK Next Plan (Matt Chotin)
http://flexorg.wip3.adobe.com/gumbo/gumboplan.htm
Flex 4 Skinning Architechture : Deepa Subramaniam
http://bit.ly/46xv4V
Designer / Developer Workflow in Flex 4 (Ely Greenfield)
http://bit.ly/zM2h2
Feature Specifications
View all specifications.
- FXG 1.0 (Graphic Interchange Format)
- Skinning and Skinnable Components
- Enchanced States Syntax
- Group Containter
- Items Component and Selector
- Layout Interface
- Application Component
- Text Primitives
- TextInput Component
- TextArea Component
- ScrollBar Component
- Range Class
- Track Base Class
- Slider Component
- Spinner Component
- Numeric Stepper Component
- MXML 2009
Podcast : The Future of Flex : Matt Chotin on the Flex Show
http://www.theflexshow.com/blog/index.cfm/2008/7/30/The-Flex-Show–Episode-49-The-Future-of-Flex-with-Matt-Chotin
More Resources
Flex Developer Forums
http://www.adobeforums.com/webx/.3c060f85/
Flex Team Blog
http://blogs.adobe.com/flex/
Sean Moore also has a good link round up on his blog.