Middleman is a static site generator based on Sinatra. Providing dozens of templating languages (Haml, Sass, Compass, Slim, CoffeeScript, and more). Makes minification, compression, cache busting, Yaml data (and more) an easy part of your development cycle.

A Beautiful Boilerplate for Responsive, Mobile-Friendly Development

Rapid Prototyping and Building Framework from ZURB

LESS Elements is a set of useful mixins for the LESS CSS pre-processor to help you cut down the size of your stylesheets

Bootstrap is a toolkit from Twitter designed to kickstart development of webapps and sites.
It includes base CSS and HTML for typography, forms, buttons, tables, grids, navigation, and more.

A folding grid for responsive design.

An WordPress Framework for designers, developers & publishers

An awesome boilerplate for responsive, cross-browser websites

Progressive flexible mobile tablet sensible extensible accessible pragmatic functional useful production-ready more

Helping your webdesign process when building sites with the brilliant Less Framework 4.

A simple CSS framework for designers and developers, based on 35 equal-width columns. It aims to cut down on development time and help you create beautiful-structured websites.

Easy is a CSS/HTML/JavaScript framework started as a personal project and then grew into something more. The idea behind it is to reduce the amount of time spent on setting up the basic master HTML template by reusing the same coding techniques.

Node's goal is to provide an easy way to build scalable network programs.

his framework has it's main focus on typography. Vertical rhythm is one of the most important things in design, so why not start your perspective from that angle?

Very nice base template framework for Wordpress.

xCSS bases on CSS and empowers a straightforward and object-oriented workflow when developing complex style cascades. Using xCSS means a dramatic cut down to your development time by: having a intuitive overview of the overall CSS structure, using variables, re-using existing style cascades and many other handy features.

Built with typographic standards in mind, Baseline makes it easy to develop a website with a pleasing grid and good typography.

Pinax is an open-source collection of integrated, but reusable apps for the Django Web Framework.

How do you scale CSS for millions of visitors or thousands of pages? Nicole first presented Object Oriented CSS at Web Directions North in Denver. Since then, the response has been overwhelming. OOCSS allows you to write fast, maintainable, standards-based front end code. It adds much needed predictability to CSS so that even beginners can participate in writing beautiful websites

The Golden Grid is a web grid system. It 's a product of the search for the perfect modern grid system. It 's meant to be a CSS tool for grid based web sites.

Build highly interactive web applications with ready-to-use widgets of the jQuery user interface library

Formy is CSS Framework for better form management.

This document proposes a XML format available to templates providers to let them list and describe their templates in a single document containing all the information needed to allow the user of a content editing environment to select, download and use a template package.

Cappuccino is an open source framework that makes it easy to build desktop-caliber applications that run in a web browser.

Emastic is a CSS Framework, it's continuing mission: to explore a strange new world, to seek out new life and new web spaces, to boldly go where no CSS Framework has gone before.

Another CSS framework. From a quick glance it looks like it's taking Blueprint and sorta building upon it and providing alot more resources to actually plan your design.

Nathan Borror doesn't like Blueprint CSS. So he created Boilerplate.