The Actionscript Virtual Machine 2 (AVM2) is going open-source with Mozilla and Adobe joining forces. Tamarin will be a model for JavaScript 2.0 and ActionScript 3.0 and any other language that is fully ECMAScript 4 compliant. It’s aim is to create a more unified scripting interface for RIAs in future, it should also enable much more ‘native’ language bridging, i.e. passing properly datatyped objects between JavaScript, ActionScript and JScript.

http://www.mozilla.org/projects/tamarin/