Prepros - Compile Less, Sass, Scss, Stylus, Jade, Coffeescript, Haml and Markdown with live browser refresh.
CodeKit - CodeKit allows you to optimize the performance of your website by automatically and efficiently compiling a variety of popular languages.
Ghostlab - Ghostlab allows you to test out a newly developed website on a variety of browsers and mobile devices at the same time. To get started, simply drag the web address to the Ghostlab system and press the play button. Read more about Ghostlab.
Fire.app - Fire.app is a menu bar only app for dead easy HTML prototyping.
Browsersync - Browsersync makes your tweaking and testing faster by synchronising file changes and interactions...
Compass CSS - Compass is an open-source CSS Authoring Framework.