http://www.jangaroo.net/home/index.html
A small demo: http://www.jangaroo.net/files/examples/flash/lines/ "Running ActionScript 3 code directly in the browser - You are implementing a Web project that must not rely on plugins and/or requires close integration into an HTML Web site, possibly already using some JavaScript framework. You want to reuse or build upon existing ActionScript 3 code (utility classes, frameworks like FlexUnit, custom code) as well as JavaScript APIs and code."
