base2 is a lightweight library that irons out all the annoying differences in JavaScript implementations. It provides the additional functionality from JavaScript 1.6+ that only Mozilla browsers implement.
Ajax GUI Framework
The Closure Compiler, Library, Templates, and Stylesheets help developers create powerful and efficient JavaScript.
MobWrite converts forms and web applications into collaborative environments. Create a simple single-user system, add one line of JavaScript, and instantly get a collaborative system.
Deep linking plugin
Processing.js is the sister project of the popular Processing visual programming language, designed for the web. Processing.js makes your data visualizations, digital art, interactive animations, educational graphs, video games, etc. work using web standards and without any plug-ins.
A Simple Standards-Based Slide Show System
ActiveJS is a JavaScript application framework that provides local and REST based data modeling and pure DOM view construction with back button and history support.
Cufón aims to become a worthy alternative to sIFR, which despite its merits still remains painfully tricky to set up and use.
Raphaël is a small JavaScript library that should simplify your work with vector graphics on the web. If you want to create your own specific chart or image crop and rotate widget, for example, you can achieve it simply and easily with this library.
CKEditor is an open source WYSIWYG text editor designed to bring common word processor features directly to web pages, simplifying their content creation. Its core code is written in JavaScript.
SVG Web is a JavaScript library which provides SVG support on many browsers, including Internet Explorer, Firefox, and Safari. Using the library plus native SVG support you can instantly target ~95% of the existing installed web base.
JS Bin is a tool for experimenting with web languages. In particular HTML, CSS and JavaScript, but JS Bin also supports other languages too (like Markdown, Jade and Sass).
JS Bin is ultimately a code sharing site.
Web Based Ajax Development Tool
Welcome to Sarien.net, the authorized portal for reliving classic Sierra On-Line adventure games. With its focus on instant fun and a unique multiplayer experience, Sarien.net hopes to win new gamers' hearts and promote the adventure game genre.
Protovis composes custom views of data with simple marks such as bars and dots. Unlike low-level graphics libraries that quickly become tedious for visualization, Protovis defines marks through dynamic properties that encode data, allowing inheritance, scales and layouts to simplify construction.
Firefox, Safari and Opera 9 support the canvas tag to allow 2D command-based
drawing operations. ExplorerCanvas brings the same functionality to Internet
Explorer; web developers only need to include a single script tag in their
existing canvas webpages to enable this support.
ActiveRecord for JavaScript (ORM)
Google Chrome Experiments is an online showroom of web browser based experiments, interactive programs, and artistic projects.
JavaScript performance tips article