As3sac is a project mainly written in ActionScript, based on the MIT license.
An AS3 implementation of the Simple API for CSS
AS3SAC is an ActionScript 3 implementation of the Simple API for CSS (provided by the W3C). In theory this should be the same reference implementation used by major browsers (though in practice... ).
More information can be found here: http://www.w3.org/Style/CSS/SAC/