Grass is an extension to CSS that allows for things such as variables, nesting, and importing of other style sheets making the web design process much more enjoyable.
python grass.py <file.grass>
This is an example that includes all the functionality of Grass.
import test2.gss
var width = 0
var red = #FF0000
.someDiv {
width: $width;
color: $red;
float: left;
li {
color: #000; // Some nested div
}
}