eCSStender - Take control of your CSS

eCSStender enables developers to patch CSS support in browsers and experiment with new features. It also enables designers to keep browser-specific hacks out of their CSS files. With eCSStender, you can take control of your CSS. 

Extensions built with eCSStender greatly simplify the design process because you can author modern CSS using advanced selectors, properties such as border-radius, or custom font faces and rest assured that your design will work... even in IE6.