Milton is a project mainly written in ..., it's free.
Milton is simple, responsive, single-column CSS framework.
It is HTML5 ready and comes in four useful widths.
768 px This handles iPads, iPhone 4s (in landscape) and any browser window with a width greater than 768 pixels.
640px A slightly smaller column for iPhone 4s in portrait.
480px (landscape) Trim a few more pixels off for non-retina iPhones in landscape.
480px (portrait) And finally handle non-retina iPhones in portrait.
Find out more at: http://ligne.in/milton