What is responsive web design? According to myself – this is from williamp.com, my own responsive site showcasing my portfolio:
It is an approach to crafting sites so that visitors have an optimized experience, one usually with no sideways scrolling, minimal resizing, and hopefully not much waiting, regardless of the device through which they visit, whether phone, tablet, laptop, desktop or something else (anyone here via web television?). It now typically embodies a mobile-first approach so that visitors using smaller viewports are given primary consideration though viewers with larger viewports may have a progressively enhanced experience, one often involving larger type and images and sometimes additional content.
Vermilion design + interactive offers this brief comparison of the big three responsive CSS frameworks. I’ve used all three and appreciate them all. I started with Skeleton and its simplicity made learning it so easy. Twitter Bootstrap has the most assets in its library currently, and I’m just finishing a new site composed with it. I like Foundation 4 because it is mobile-first by default and I think this framework is gaining momentum rapidly.