Galen Framework : Automated testing of look and feel for your responsive websites.
Layout testing seemed always a complex task. Galen Framework offers a simple solution...
Diagnostic.css : Diagnostic.css is a stylesheet which allows the user to test for common errors in a page's markup.
Also : https://github.com/karlgroves/diagnostic.css
This Is Responsive : Tips, Resources and Patterns for Responsive Web Design
Foundation : An easy to use, powerful, and flexible framework for building prototypes and production code on any kind of device.
Diffee Checker : Instant visual diffing with CSS blend modes!
Simply enter the sites you want to compare. Locally hosted addresses and files also work (so you can see ...
Breaking CSS is easy. Checking every responsive page element is hard. That’s why there's BackstopJS.