You most certainly know about Twitter Bootstrap - the popular front end framework for building websites and apps. It favors simple, responsive design, and comes bundled with a sensible default stylesheet, a number of useful jQuery plugins ...
D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG and CSS. D3’s emphasis on web standards gives you the full capabilities of modern browsers without tying yourself to a proprietary framework, combining powerful visualization components and a data-driven approach to DOM manipulation.
Smashing Magazine is an online magazine for professional Web designers and developers, with a focus on useful techniques, best practices and valuable resources.
Thimble makes it ridiculously simple to create your own web pages. Write and edit HTML and CSS right in your browser. Instantly preview your work. Then host and share your finished pages with a single click. Easy, huh?