CSS preprocessor. Written in PHP
The CssSelector component converts CSS selectors to XPath expressions.
An easy to use stand-alone PHP-Library (but at the same time also a Wordpress plugin) that combines, optimizes, dataURI-fies, re-splits, compresses and caches your CSS and JS for quicker loading times.
A Parser for CSS Files written in PHP. Allows extraction of CSS files into a data structure, manipulation of said structure and output as (optimized) CSS
RTLCSS-PHP is a framework for converting LTR CSS to RTL.
Compiles SASS to CSS automatically with pure PHP. No ruby used. One line of code. Currently uses latest SCSS 3.2 syntax, imports and mixins. Compass can also be used.
Assets manager for PHP. Allow manage CSS and JS files in website and its dependencies. Also allows refresh cache in browsers by adding revisions of loaded files. Builtin plugins to compile SASS and/or LESS styles to CSS just-in-time.
CssToInlineStyles is a class that enables you to convert HTML-pages/files into HTML-pages/files with inline styles. This is very usefull when you're sending emails.