Responsive Web Design Weekly A free weekly round up focused on everything and anything to do with Responsive Design. Article
Jarallax An open-source javascript library which makes adjusting css based on interaction easy. Javascript
jsFiddle Allows you to code HTML, CSS, and Javascript in one window and see your results instantly. CSS HTML Javascript Testing Tools
circuits.io Free circuit editor in your browser. 123D Circuits is an open hardware community providing free collaborative circuit design tools and easy PCB manufacturing. Tools