Review: Free mobile-friendly Web design frameworks
Twitter Bootstrap, HTML5 Boilerplate, 52Framework, and 320 and Up take the sting out of building websites for both large and small screens
52framework bills itself as "the framework from the future," which in this case means support for HTML5, CSS3, and all the cutting-edge features associated with those things. 52framework is most useful for getting a leg up with advanced HTML5 features, especially the likes of video and local storage, and for having frameworks for handling form inputs. It's less effective for building a design that's both mobile- and desktop-friendly, since other frameworks here have more pieces for those tasks.
Most of the pieces inside 52framework should be familiar: It uses Modernizr and Selectivizr for backward compatibility, sports a grid-layout system, and provides a broad range of CSS3 property controls. What I found most lacking in 52framework was the documentation. Instead of textual documentation, as with Bootstrap and Boilerplate, you'll find a series of YouTube-hosted video demonstrations. They're useful as adjuncts to existing documentation, but not a substitute for it.
That said, there are demo and example pages that at least serve as quick references to the native styles in the framework, but a more robust option would be nice to have. I liked the included Photoshop and Illustrator design templates, which make it easier to use those programs to plan designs using the framework.
52framework is free under the Creative Commons CC-BY-SA 3.0 license.