5 Most Popular HTML5 Responsive Frameworks

HTML5 Boilerplate

Boilerplate is not a framework, nor does it prescribe any philosophy of development, it's just got some tricks to get your project off the ground quickly and right-footed.

(html5boilerplate.com)

Although it is not a framework I decided to mention it first because it is good starting
point for any HTML5 project.

It contains features that others don’t have e.g. cross-browser normalization,
performance optimizations, even optional features like cross-domain XHR and Flash.

Twitter Bootstrap

Twitter Bootstrap is a free
collection of tools for creating websites and web applications. It contains HTML and CSS-based design templates for typography, forms, buttons, charts, navigation and other interface components, as well as optional JavaScript extensions.
(en.wikipedia.org/wiki/Twitter_Bootstrap)

Bootstrap is made with LESS at its core.

I like its 12-column grid system and amazing Javascript plugins, such as modal windows, tooltips, carousel and others.

Zurb Foundation

Foundation is the most advanced responsive front-end framework in the world. With Foundation you can quickly prototype and build sites or apps that work on any kind of device, with tons of included layout constructs (like a full responsive grid), elements and best practices.
(github.com/zurb/foundation/blob/master/README.md)

It’s a bit ambitious, isn’t it? I can only add it’s built with Sass.

Skeleton

Skeleton is a small collection of CSS files that can help you rapidly develop sites that look beautiful at any size, be it a 17" laptop screen or an iPhone.
(www.getskeleton.com)

I met some commercial templates that are built on Skeleton.

HTML KickStart

HTML KickStart is an ultra–lean set of HTML5, CSS, and jQuery (javascript) files, layouts, and elements designed to give you a headstart and save you 10's of hours on your next web project.
(www.99lime.com)