Writing an interpreter or a compiler is one of the most educational tasks in programming because you can become familiarized with the details of the code interpretation and evaluation process. You can obtain much deeper knowledge of what sorts of things are going on behind the scenes and gain some insights into the decisions behind language design.

A new way to build apps.
Meteor is a set of new technologies for building top-quality web apps in a fraction of the time, whether you're an expert developer or just getting started.

Mocha is a feature-rich JavaScript test framework running on node and the browser, making asynchronous testing simple and fun. Mocha tests run serially, allowing for flexible and accurate reporting, while mapping uncaught exceptions to the correct test cases. Hosted on GitHub.

A great intro to animation in JavaScript. Really made sense.

Smashing Coding

Skeleton is a small collection of CSS & JS files that can help you rapidly develop sites that look beautiful at any size, be it a 17" laptop screen or an iPhone.

AmplifyJS is a set of components designed to solve common web application problems with a simplistic API. Amplify's goal is to simplify all forms of data handling by providing a unified API for various data sources. Amplify's store component handles persistent client-side storage, using standards like localStorage and sessionStorage, but falling back on non-standard implementations for older browsers. Amplify's request adds some additional features to jQuery's ajax method while abstracting away the underlying data source.

A great little standalone PubSub JS lib.