A better way to use localStorage and sessionStorage
CSS Parent Selector
CSS4 parent selector based on jQuery
Small, fast, awesome. The only ES5-ish set of polyfills (shims) you can mix-and-match because they're individual AMD modules.
Tiny polyfill for the placeholder form element attribute. Requires Prototype.js.
This script is the defacto way to enable use of HTML5 sectioning elements in legacy Internet Explorer.
A lightweight engine that allows you to hitch new capabilities to the browser (prollyfill).
Tired of adding prefix for each broswer when it comes to the new css3 attributes?
A fast & lightweight polyfill for min/max-width CSS3 Media Queries (for IE 6-8, and more)
JS string formatter that supports objects, currency, date/time, decimals, and more supports easy extension and garbage collection ... goes far beyond sprintf approach.
An Asynchronous Conditional Resource Loader
Legacy support for the CSS3 Flexible Box Model