melonJS is the result of our enthusiasm and past experiments with Javascript, and came from the feeling that no simple, free and standalone library was available to develop games. And although still a big work in progress (and not yet bug free), melonJS already allows to easily create some nice games (see the Gallery page)
AJAXSLT is an implementation of XSL-T in JavaScript, intended for use in fat web pages, which are nowadays referred to as AJAX applications. Because XSL-T uses XPath, it is also an implementation of XPath that can be used independently of XSL-T.
Underscore is a utility-belt library for JavaScript that provides a lot of the functional programming support that you would expect in Prototype.js (or Ruby), but without extending any of the built-in JavaScript objects. It's the tie to go along with jQuery's tux, and Backbone.js's suspenders.