DOMAssistant : The modular lightweight JavaScript library, with CSS selectors, event handling, AJAX and complete Unicode support
InstantClick : InstantClick is a JavaScript library that dramatically speeds up your website, making navigation effectively instant in most cases.
MooTools : MooTools is a compact, modular, Object-Oriented JavaScript framework designed for the intermediate to advanced JavaScript developer. It allows you to ...
ClippyJS : Add Clippy or his friends to any website for instant nostalgia.
dancer.js : dancer.js is a high-level audio API, usable with both Mozilla's Audio Data API and Webkit's Web Audio API with flash fallback, designed to make sweet ...
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.