Alessandro Carbone

How many times have you wished to minify in a clean way all the stylesheets and scripts of a WordPress website?
AssetsMinify takes every CSS and JS asset included using <code>wp_enqueue_style()</code> and <code>wp_enqueue_script()</code>, merges and minifies them.
You can also use AssetsMinify to create your WP theme using Compass / Sass / Less without configuring any <code>config.rb</code> or that kind of stuff.
AssetsMinify is based on Assetic library.
<a href="https://github.com/acarbone/AssetsMinify" rel="nofollow ugc">Fork me on Github</a>.

AssetsMinify

Use Compass, Sass, Less, Stylus, CoffeeScript (and more ...) to develop your themes and minify your stylesheets and JavaScript.

Bytes.co

Harness the power of pre-processed CSS and minified JS in your theme or plugin, without any complicated installs or build tools. Simply tell WP Compiler where to find your source files and where to put the compiled results, then throw your install into Dev Mode. WP Compiler watches your source folders for you, and recompiles your CSS and JS on any file change. WP Compiler supports both SCSS and LESS precompilers for CSS, to suit anyone’s preference.
When you’re ready to launch a new site, just turn off Dev Mode, and your styles and javascript will be compiled & minimized and comments & source maps will be removed. With Dev mode disabled, Compiler will stop watching source directories, so there is no effect on site performance, but you can still apply a quick change at any time, by clicking the compile button in the admin toolbar.
WP Compiler relies on <a href="http://leafo.github.io/scssphp/" rel="nofollow ugc">scssphp</a>, <a href="http://lessphp.typesettercms.com/" rel="nofollow ugc">lessphp</a>, and <a href="https://www.minifier.org/" rel="nofollow ugc">minify</a>. 
Specific issues with the underlying compilation libraries should be submitted to their respective developers.

WP Compiler

Harness the power of pre-processed CSS and minified JS in your theme or plugin, without any complicated installs or build tools.

AssetsMinify vs WP Compiler