CodeKit - CodeKit allows you to optimize the performance of your website by automatically and efficiently compiling a variety of popular languages.
CSS Scan - Instantly check or copy computed CSS from any element for only ~95$
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.
Hoverify - All-in-one browser extension to improve your web dev experience.
Browsersync - Browsersync makes your tweaking and testing faster by synchronising file changes and interactions...
CodePen - A front end web development playground.