Backbone supplies structure to JavaScript-heavy applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions, views with declarative event handling, and connects it all to your existing application over a RESTful JSON interface.
The project is hosted on GitHub, and the annotated source code is available, as well as an online test suite, an example application and a list of tutorials.
Link: GitHub
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.
Underscore provides 60-odd functions that support both the usual functional suspects: map, select, invoke — as well as more specialized helpers: function binding, javascript templating, deep equality testing, and so on. It delegates to built-in functions, if present, so modern browsers will use the native implementations of forEach, map, reduce, filter, every, some and indexOf.
A complete Test & Benchmark Suite is included for your perusal.
You may also read through the annotated source code.
Link: GitHub
MooTools is a compact, modular, Object-Oriented JavaScript framework designed for the intermediate to advanced JavaScript developer. It allows you to write powerful, flexible, and cross-browser code with its elegant, well documented, and coherent API.
Link: MooTools
It’s true. The world needs another JavaScript DOM Selector Engine. So without further fuss – introducing Qwery – The Tiny Selector Engine. It’s a port from where Simon Willison left off with his getElementsBySelector in 2003, and believe it or not, this is exactly where jQuery started.
Qwery supports all the basic CSS1 & CSS2 selectors, plus the additional (most important) attribute selectors from CSS3. Additionally it allows multi-selects (div,p) as well as context-aware selectors (like jQuery.find()).
Last but not least, it’s open source awaiting your valuable feedback to make it leaner and faster. There are tests to ensure its integrity, however sans-benchmarks. Although, it should be noted it does support querySelectorAll when available in the browser (to bring 2003 to modern times).
Link: Dustin Diaz