Prototype : Easy Ajax and DOM manipulation for dynamic web applications
Web Forms : Web Forms 2.0 Cross-Browser Implementation
Sammy.js : Sammy is a tiny javascript framework built on top of jQuery, It's RESTful Evented Javascript.
Processing.js : Processing.js is the sister project of the popular Processing visual programming language, designed for the web. Processing.js makes your data visuali...
Aloha Editor : Aloha Editor is an open source WYSIWYG editor that can be used in webpages. Aloha Editor aims to be easy to use and fast in editing, and allows advanc...
Rainbow is a code syntax highlighting library written in Javascript.
It was designed to be lightweight (1.4kb), easy to use, and extendable.
It is completely themable via CSS.