The YUI Library provides tools for professional web development, including a rich JavaScript and CSS library -- all freely available under a liberal BSD license.
Dojo saves you time, delivers powerful performance, and scales with your development process. It’s the toolkit experienced developers turn to for building superior desktop and mobile web experiences.
MochiKit is a highly documented and well tested suite of JavaScript libraries that will help you get things done, fast. It takes good ideas found in Python, Objective-C, etc. and adapts them to the crazy world of JavaScript.
Welcome to the Yahoo! Design Pattern Library. We look forward to your feedback. (A pattern describes an optimal solution to a common problem within a specific context.)
qooxdoo is an advanced open-source JavaScript-based GUI framework. It helps you to implement AJAX-enhanced web 2.0 applications - easier than ever before.