CSS Parent Selector
CSS4 parent selector based on jQuery
Xdate
A Modern JavaScript Date Library
String.js
Extra JavaScript string methods.
Typecast.js
Typecast.js :: Solving the simple problems
Selectivizr
Selectivizr is a JavaScript utility that emulates CSS3 pseudo-classes and attribute selectors in Internet Explorer 6-8.
Respond
A fast & lightweight polyfill for min/max-width CSS3 Media Queries (for IE 6-8, and more)
Moment
Parse, validate, manipulate, and display dates in javascript.
Numeral
A javascript library for formatting and manipulating numbers.
Placeholder Shiv
Tiny polyfill for the placeholder form element attribute. Requires Prototype.js.
HTML5shiv
This script is the defacto way to enable use of HTML5 sectioning elements in legacy Internet Explorer.
Xregexp
Extended JavaScript regular expressions
Yepnope.js
An Asynchronous Conditional Resource Loader
Flexie
Legacy support for the CSS3 Flexible Box Model
ES5 Shims
ECMAScript 5 compatibility shims for legacy JavaScript engines
Datejs
Datejs is an open-source JavaScript Date Library.
CSS3 Pie
A behavior for Internet Explorer allowing it to recognize and render various CSS3 box decoration properties
Css3 Finalize
Tired of adding prefix for each broswer when it comes to the new css3 attributes?