Actually, I was talking about Java, not JavaScript.
Java is the dominant language on Android (though there's a native SDK written in C++), so it'd be the target for most GUI and game-development code. Having a tweening library available in Android would be spectacular.
Of course, I understand the differences between Java (class-based inheritance) and ActionScript (prototype-based inheritance), so I'm well-aware that a tweening library for Java would be a somewhat different animal. I was just curious to know whether you'd considered it.