Javascript Component Library - ActiveWidgets 2.5.

ActiveWidgets is a powerful javascript component library which makes web application development (especially AJAX-style apps) a lot easier and more productive. ActiveWidgets provides you with a set of common visual elements (like datagrid, tabs, tree, combo) sharing professional look-and-feel and simple programming model.

网站：http://www.activewidgets.com/

就不翻译了，最大的好处是提供试用版下载，可以好好研究一下实现原理。