ActionScript is the ScriptingLanguage used in MacromediaFlash. Because it is closely based on ECMAScript, it has many of the same strengths and weaknesses expressed in JavaScriptRocks and JavaScriptSucks.

Short history of ActionScript
* Flash 2: Basic, simple "actions" like moving to a specific frame of an animation
* Flash 4: Introduced variables, control flow, CGI communication
* Flash 5: Reorganized language to be more similar to JavaScript
* Flash 7: Introduced classes, methods, and inheritance (ActionScript 2.0)

ActionScript 3.0 is currently in public alpha, and introduces the following:
* Based on current working proposal for ECMAScript edition 4.
* Has a StronglyTyped compiler with keywords that allow for WeaklyTyped runtime checking of types.
* Improved support for LexicalClosure''''''s
* A new VirtualMachine with incremental GarbageCollector and JIT compilation

see http://labs.macromedia.com/.

There have been some efforts to build a TestingFramework for ActionScript (to be called AsUnit, of course), but so far nothing has come of it.

There is a Wiki devoted to ActionScript at http://chattyfig.figleaf.com/flashcoders-wiki/index.php

See http://www.actionscripts.org http://www.flashkit.com

There is now a rather nice TestingFramework for MacromediaFlash 7 (Flash MX Pro 2004) called AS2Unit.  It is specifically designed for the above version of Flash since it includes project level functionality, source code control, etc.
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It's fantastic to see the powerful (if poorly specified) ECMAScript language used outside of web design. Would that it were being used somewhere where it isn't specifically for the use of non-programmers, resulting in the same sort of crud:

 for(i = 0; i < num_boxes; i++){
  box = eval("root.myBox" + i);
  box.text = eval("boxText" + i);
 }

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See http://www.as2unit.org/
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CategoryProgrammingLanguage