Trionic Labs

SASS is a programmable approach to stylesheets which really adds some cool features. It can make a stylesheet easier to read, easier to update and also adds some powerful features like functions, variables and imports. (See http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html for more details.)
This plugin enables any WordPress Theme to use SASS stylesheets. In a wordpress theme, the comments at the top of style.css are used to define the theme. For this reason, this plugin will not allow a .sass or .scss file named ‘style’.

WordPress SASS

This plugin provides automated SASS stylesheet generation.

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.

WordPress SASS vs WP Compiler