HTML5 Boilerplate!

Materialize is a modern responsive CSS framework based on Material Design by Google

Flat UI Pro is made on the basis of Twitter Bootstrap in a stunning flat-style, and the kit also includes a PSD version for designers. Flat UI Pro contains a huge number of basic components, icons and glyphs.

An implementation of Material Design components in vanilla CSS, JS, and HTML.

HTML KickStart is a ultra–lean set of HTML5, CSS, and jQuery (javascript) files, layouts, and elements designed to give you a headstart and save you a lot of hours on your next web project.

Sassy-validation is a Sass data type validation library.

The Fluid 960 Grid System templates have been built upon the work of Nathan Smith and his 960 Grid System using effects from the MooTools and jQuery JavaScript libraries. The idea for building these templates was inspired by Andy Clarke, author of Transcending CSS, who advocates a content-out approach to rapid interactive prototyping, crediting Jason Santa Maria with the grey box method.

Foldy960 - A responsive version of the 960 grid, the Pvel way!

Unsemantic is a fluid grid system that is the successor to the 960 Grid System. It works in a similar way, but instead of being a set number of columns, it's entirely based on percentages.

Although the overall look and feel are most definitely inspired by Twitter Bootstrap, Cascade framework is not just another Bootstrap clone. Where Twitter Bootstrap puts its focus on delivering shiny user elements that can be dropped into any project and takes control of your project's overall look-and-feel, Cascade Framework is intended to do the opposite. By splitting your CSS into separate files based on features rather than selectors as well as by implementing a modifier design pattern inspired by SMACCS and OOCSS, Cascade Framework puts you in control! »

Google's material design UI components built with React.