Some open-source flex/flash Projects

Adobe APIs
It mainly includes corelib, mappr, Flickr, YouTube, encryption, and other class libraries.
Http://labs.adobe.com/wiki/index.php/Actionscript_3:resources:apis:libraries

As3awss3lib
The ActionScript 3.0 class library that interacts with Amazon S3
Http://code.google.com/p/as3awss3lib/

As3soundeditorlib
Sound editing class library
Http://code.google.com/p/as3soundeditorlib/

As3ds
As3 data structure for game developers
Http://code.google.com/p/as3ds/

Mecheye-as3-libraries
GroupFlashGame DevelopmentAs3Class Library.

Http://code.google.com/p/mecheye-as3-libraries/

Ape
Simulation physical engine API of ActionScript
Http://www.cove.org/ape/

As3crypto
Password System Library implemented in as3, supportedAlgorithmIncluding RSA, AES, Des, 3DES, md2, MD5, SHA-1, SHA-224, SHA-256, etc.
Http://crypto.hurlant.com/

Fzip
This allows as3 to load data in the standard ZIP format and decompress the files.
Http://codeazur.com.br/lab/fzip/

3D

Ascollada
An as3 class library that parses the Collada file format. Collada is an open source code project that allows 3D data to be stored in XML format and allows 3D users to easily carry and exchange data.Materials

Http://code.google.com/p/ascollada/

Away3d
3D Engine
Http://code.google.com/p/away3d/

Papervision3d
3D Engine
Http://code.google.com/p/papervision3d/

UI-related projects

Uicomponents-as3
A lightweight as3 UI Component Library
Http://code.google.com/p/uicomponents-as3/

Tweener
Full featured animation library
Http://code.google.com/p/tweener/

Asinmotion
One of as3AnimationClass Library, which can run parallel or linear Management special effects.

Http://code.google.com/p/asinmotion/

Flest
Ria enterprise-level as3 applicationsProgramDevelopment Framework, with the application of controller, factory, command, etc.DesignAnd adopts efficient, concise, and practical pipe-type design features.

Http://code.google.com/p/flest/

APIS of third-party companies or tools

Yahoo as3 APIs
Http://developer.yahoo.com/flash/as3_api_libraries.html

Facebook-as3
Access the as3 API of the Facebook platform
Http://code.google.com/p/facebook-as3/

Salesforce flex Toolkit
Http://wiki.apexdevnet.com/index.php/Flex_Toolkit

Twitter as3 API
Http://twitter.com/blog/2006/10/twitter-api-for-flash-developers.html

Xiff
XMPP client library
Http://svn.igniterealtime.org/svn/repos/xiff/branches/xiff_as3_flexlib_beta1/