I just read about a new JavaScript framework today:
Fast and flashy: Famo.us JavaScript framework revealed (InfoWorld.com)
From the article and the subsequent code demo page, it looks like a GUI framework written in JavaScript that uses WebGL + HTML + CSS3 transformations as the display layer, rather than the normal HTML + CSS combo.
They are claiming near native-speed performance. The framework is in a private alpha phase. If it becomes all they say it will, it could be seen as a viable cross browser, cross platform replacement for Flash.