Legacy support for the CSS3 Flexible Box Model
Tiny polyfill for the placeholder form element attribute. Requires Prototype.js.
CSS4 parent selector based on jQuery
An Asynchronous Conditional Resource Loader
Tired of adding prefix for each broswer when it comes to the new css3 attributes?
Allows for automatic Image fallbacks for browsers that can't handle SVGs
Small, fast, awesome. The only ES5-ish set of polyfills (shims) you can mix-and-match because they're individual AMD modules.
A lightweight engine that allows you to hitch new capabilities to the browser (prollyfill).
A better way to use localStorage and sessionStorage
A behavior for Internet Explorer allowing it to recognize and render various CSS3 box decoration properties
JS string formatter that supports objects, currency, date/time, decimals, and more supports easy extension and garbage collection ... goes far beyond sprintf approach.
A fast & lightweight polyfill for min/max-width CSS3 Media Queries (for IE 6-8, and more)