Voxelcss is an open-source, in-browser 3D rendering engine built entirely using CSS.
Milligram is a minimalist CSS framework. It includes typography, buttons, forms, grids, and more.
Bulma is a modern CSS framework based on Flexbox. It uses a simple grid system, a flexible navbar, and versatile media objects, among other features.
Min is a very inclusive CSS framework that supports even 5.5 versions of Internet Explorer, as well as FF3 , Opera 9 , and Safari 4 , unlike bootstrap, it doesn’t prescribe a certain design for you and it features clear and short class names.
StringBean is a featherweight CSS framework that comes in at just 4K. It uses a 24-point grid system rather than the more common 12-point.
RichCSS is a clean and reusable object oriented CSS framework. It allows for reusability of your CSS, versioning, and more.
Outline is a simple and clean CSS framework that works as a starter boilerplate for new web projects. It features full responsiveness, Sass coding, modular building and Susy grids on demand.
A Beautiful and Full-featured CSS Framework,A CSS framework which combines Blueprint and Tripoli to extend functionality. It is mainly focused on the graphic part of the website, including images and stylesheets for your site structure. It was made by Mike Crittenden, licensing it under modified MIT and GNU.
If you’re building a site that doesn’t need too many app-specific UI components, then Base is a fantastic resource. Pages built with it already look pretty; but if you don’t like the default styles, it’s not too difficult to change them.
Kube is definitely a tool for the modern front-end developer. Only modern browsers—and IE9+—are supported. The default styles are pretty, but bland enough to be adapted for use with almost any branding.
It is, in short, a good-looking but plain and simple framework, designed with near-universal visual appeal, and meant for heavy customization.
Out of the box, Blaze CSS is already lightweight, but you can reduce its file size even more due to its modular architecture which allows you to include only the parts you intend to use in your project. (Read the instructions for creating a custom Blaze CSS build for more info.)
Pure, an open source project led by Yahoo! developers, is a suite of CSS modules that will help you quickly build responsive web designs. Pure has basic styles for all HTML elements (developed on top of Normalize.css), and modules for grid layouts, web forms, buttons, tables, and navigation menus.
Picnic CSS is a lightweight UI framework written in Sass, making it easier for you to edit and customize variables such as colors and lengths. It also has some impressive, purely-CSS UI components such as a modal window and a content slider.
Siimple is a minimalist CSS framework for building responsive, clean web designs. It’s similar to Skeleton: It has an intuitive 12-column grid system and base styles for typography, tables, buttons, forms, and more.
Though it hasn’t been updated in over a year, Skeleton is still a top-notch starting point/boilerplate for rapidly building modern, responsive web designs. It comes with an intuitive grid system and base styles for your HTML elements.