These are either AS3 utility libraries or flex UI component libraries.
- as3corelib: Contains a bunch of useful stuff like MD5 and SHA hashing, VCard parsing, jpeg and png encoding, JSON support and utilities for working with arrays, dates, numbers, strings and xml. Seems to be Adobe contributed code.
- flexlib: A lot of nice UI components and stuff, like the TreeGrid. Also with some Adobe contributions.
- alivepdf: A way to produce pdf output via as3 code. Not sure where I would use that. Maybe if someone needed to off-load the server from the task. Maybe it is most useful in AIR applications and not so much in the more constrained flex sandbox.
- actionscript3libraries: A nice list of others over at http://riaforge.org/.
- tweener: Doing animations using code to move things instead of being forced into the flash timeline model.
- flexvizgraphlib: A really interesting library with which you can do data visualization in flex
These are not simply libraries of functionality, but whole frameworks that tries to help you structure your complete flex application into something manageable. Mostly helpful when your flex application gets really large, I think. These are about application architecture.
- Cairngorm: A MVC based framework. Done by Adobe themselves.
- PureMVC: Another MVC based framework
- Model-Glue: Well, yet another MVC based framework :-)
- ARP: A pattern based framework.
- Flest: Hmm, a MVC looking framework which claims not to be an MVC implementation
- Foundry: Interesting in that in includes a Java/server-side part, which claims to aid in FDS server development. Not important for dudes like me, which try to avoid FDS, though.
Some libraries that aid in automatic testing of your flex applications.
- flexunit: JUnit based API. Not dependent on payware.
- funfx: Write your tests in the nice ruby language. Uses the automation package of FDS to remote control the application when doing automatic testing, which leads to the need of a license on FDS (payware).