Useful Actionscript Libraries and Utilities
If you have been working with actionscript for a while you should know that the main goal should not just be to "make it work" but to make sure that you are your code is implemented following the rules of simplicity, clarity and elegance. This is not always easy to achieve especially when you have to work under strict deadlines.
Personally I don't have time to reinvent the wheel every time I start working on a new project and I try to reuse as much as possible classes and utilities I have already developed (when I had the time to do so). But since our days just have 24 hours we don't always have the time to create a particular class utility or API for a particular project therefore it is always precious to know that there is an existing gold mine of existing utilities which are freely available over the internet.
I though it would be very informative to give you a list of class, APIs and utilities that I have been and am still using in order to simplify my life as a developer, the list below will be updated regularly, also don't hesitate to drop a comment at the bottom if you found something useful that would deserve to be added to the list.
If you have been coding in the default Flash actionscript panel until now it might be time to review the situation because there is better solutions out there.
Flashdevelop is my prefered actionscript editor for the main reason that it enhances my productivy massively, the only downside for now is that it does not has a refactoring and autoformat utility. When I need to do that I will use Flex in parallel. In any case I will favor Flashdevelop over any other actionscript editor.
FDT3 is a dedicated actionscript editor built on Eclipse, it is a powerful editor and it has many features that Flashdevelop does not have but I am not a big fan of Eclipse and therefore this wasn't my first choice. Also FDT is fairly expensive while Flashdevelop is free (donations warmly accepted if you like it) I recommend you have a look at it and install the 30 days demo.
Although I am not a big fan of Eclipse I would still recommend that you learn to use Flex and FDT since those two applications are used extensively in the Flash industry and you will need to know how to use them if you want to raise your chances to get a job in the Flash and Flex industry :)
I am not going to write much about Flex here because it is more than a coding environment and I have already wrote and article on Flash and Flex
There are other actionscript editors out there that you might want to have a look at, there are not in my favourite list because they either lack support for AS3 or are don't fit my needs but since we all have different tastes and needs you can also have a look at: Sepy, PrimalScript, ASDT.
APIs and Libraries
If you are not satisfied with the default built in Tween class here are other potential choices you might want to have a look at:
TweenMax (AS3 and AS2) if you are looking for an easy way to tween with code look no further, I am using it regularly.
Tweensy (AS3) is another popular choice which is (not verified personally) apparently faster than TweenMax, contained within Tweensy is an expansion package called Tweensy FX which allows for motion effects to be applied onto DisplayObjects. Tweensy is more dedicated to bitmap and particle rendering.
Tweener(AS2, AS3) is another solid contender that I used in the past and is still regularly updated
AS3 animation system 2.0, I haven't tried that one personally but if it does what's written on the tin it sounds very promising.
GOASAP, here is an interesting generic base library for building animation tools in ActionScript 3.0, if you are looking for something simple this is probably not for you but if you are serious about advanced development and flexible approaches to animation it might be worth a look.
GTween (AS3) is another interesting tweening engine, still in beta but promising.
Twease is another lighweight tweening engine for AS2 and AS3
Flash and 3D
Papervision3D is an Open Source realtime 3D engine for Flash, it is probably the oldest one and you will find plaenty of tutorials around to get you started.
Sandy Sandy is a Flash 3D engine, available for and AS2, AS3.
Away3D is another popular 3D engine for Flash.
Alternativa3D is an impressive 3d engine for Flash, the 2 demos on their homepage are really worth checking.
Coppercube is a commercial application still in beta stage that let you create 3d scenes and animations for Flash using a WYSIWYG editor and "without programming",you can import your 3D models into the CopperCube editor and publish them directly as Flash .swf file for websites or as standalone windows .exe file.
Flash will never try to compete with the big 3d softwares like Lightwave, Maya or 3DSmax and it is not recommended to develop highly complex 3d worlds in Flash because you will never achieve what can be done with those dedicated 3d applications, nevertheless those engines are very useful when you want to add an extra touch of 3D to you projects.
The corelib project consists of several basic utilities for MD5 hashing, JSON serialization, advanced string and date parsing, and more.
FlexUnit is a unit testing framework for Flex and ActionScript 3.0 applications. It mimics the functionality of JUnit, a Java unit testing framework, and comes with a graphical test runner.
The Flickr library is an ActionScript 3.0 API for the online photo sharing application, Flickr. It provides access to the entire Flickr API.
Mappr is a service and application that combines images from Flickr with geolocational information. The Mappr ActionScript 3.0 API gives you access to Mappr's geo-tagged image data.
RSS and Atom libraries
Use the RSS and Atom libraries to parse Atom and all versions of RSS easily. These libraries hide the differences between the formats so you can parse any type of feed without having to know what kind of feed it is.
The YouTube API provides an ActionScript 3.0 interface to search videos from YouTube.
This ActionScript API provides a number of utilities for manipulating and adding content to maps through a variety of services, enabling you to embed robust, interactive maps applications on your website or in desktop applications.
SWC for Flash and Flex 3 enables you to add a map to a wide range of web and desktop applications. Included in the API is support for other Yahoo! APIs including geocoding, local search and traffic APIs along with an advanced marker and overlay system to allow you to easily render geo-data on the map.
The eBay ActionScript 3.0 library provides an interface between the eBay XML API and ActionScript 3.0. This open-source library will allow developers to create novel and innovative applications leveraging both eBay's marketplace services and Adobe's Flash Player 9 runtime! It is written in ActionScript 3.0, so any environment using ActionScript 3.0 can use this library, including Adobe Flex 2 and Adobe Flash Pro 9.
This article will be regularly updated.