Organize your CSS as reusable components. Components are built up of parts (child elements), parts are included using __part-name. Components are flexible with options (like arguments; class="component-name --option). Tweaks are small changes applied using a + sign. You can watch a related Laracast here.

Bootstrap-like framework with focus on Google's Material Design look and interactions. Forms section is a great example of how nice it can look. Sass available, and several Javascript components.

Need to showoff what your website/app looks like, use this to make it look like it's on an iphone or ipad using just CSS.

A robust mixin library with 86 mixins for everything from border-radius to Flexbox and css animations.

Silky smooth parallax effect using only #css (hit the debug button for awesomeness) http://blog.keithclark.co.uk/wp-content/uploads/2014/08/demos/3/

Get a lot of comps from designers in PSD? Then have to either install Photoshop and look up sizes to implement it or just guess? This pretty neat tool from the creators of that format, allows you to easy get those values out of a PSD all online, even converts the objects to css (eg. the font-family to use, etc).

Refill is a collection of examples of web components you can use for Bourbon (Sass mixins library) similar to say, Bootstrap's components.

Library of some pretty slick animations using only css3 (no js).

Basically a Bootstrap theme with some really nice css and color tweaks.

Rachet is a css framework to quickly prototype an app before you build it natively. Or maybe you decide to make your native app a webapp wrapper, you can build the whole thing on Rachet. Rachet recently got folded into the Bootstrap Organization.

A bunch of cool, fun, and cross-browser animations for you to use in your projects. Great for emphasis, home pages, sliders, and general just-add-water-awesomeness.

Powerful, scalable, Sass-based, BEM, OOCSS framework by Harry Roberts aka csswizardry.

A small framework that provides an easy-to-use API for building pages with for synchronizing video and CSS3 animations. Great intro to it on http://coding.smashingmagazine.com/2013/11/18/the-future-of-video-in-web-design/

Great example of how we'll soon be able to shape text to flow around non-rectangular shapes. Just watch the video, I installed Chrome Canary and tried out the demo and it didn't seem as smooth for me. Also, I'm not a fan of having animations tied to mouse scroll, I never seem to scroll the right amount.

Adobe and Ultranoir team up to experiment with building a richer storytelling experience.

Learn more here: http://blogs.adobe.com/webplatform/2013/10/23/css-shapes-visual-storytelling/

It's a set of small, responsive CSS modules. Just 5.7KB (smaller if you only use a couple). Includes a grid framework and styles for forms, buttons, tables and menus. It follows the SMACSS concept for modules. Use Skin Builder to customize the feel. If you think Bootstrap enforces too much of a particular look, this may be for you. Pure even works with Bootstrap JS modules.

Forget LESS and Sass, FESS is the way to go now http://t.co/fynl8fPndJ #css

Assetic combines two major ideas: assets and filters. The assets are files such as CSS, JavaScript and image files. The filters are things that can be applied to these files before they are served to the browser. Assetic was created by a member of the core Symfony team and is part of the official Symfony Cookbook: http://symfony.com/doc/master/cookbook/assetic/asset_management.html

Introducing Brackets a new open source code editor for the web. -- http://github.com/adobe/brackets

So your working on your WordPress theme, and need to include some javascript or css, just throw it in the header or footer right? Well, actually Wordpress has it's own preferred way of including js and css. If you follow their best practices, you can avoid the risk of conflicting with other themes and plugins.