Opacity. Gradients. Drop shadows.
Long before CSS proposals for Transitions and Transforms, Internet Explorer 4 supported visual special effects through CSS. This capability was further extended by Internet Explorer 5.5. As an example, the following rule could be used to apply opacity to an object:
http://blogs.msdn.com/ie/archive/2009/02/19/the-css-corner-using-filters-in-ie8.aspx
