String.js
Extra JavaScript string methods.
Poly
Small, fast, awesome. The only ES5-ish set of polyfills (shims) you can mix-and-match because they're individual AMD modules.
Object.observe
Object.observe polyfill/shim trying to be compliant
Timezone Js
Timezone-enabled JavaScript Date object. Uses Olson zoneinfo files for timezone data.
Date
Date() for humans
Numeral
A javascript library for formatting and manipulating numbers.
Core Lib
A port of the Ruby 1.9.3 corelib to coffeescript/javascript/node that conforms to rubyspec.org.
Placeholder Shiv
Tiny polyfill for the placeholder form element attribute. Requires Prototype.js.
Dayjs
⏰ Day.js 2KB immutable date library alternative to Moment.js with the same modern API
Sugar
A Javascript library for working with native objects.
Klass
a utility for creating expressive classes in JavaScript
Xdate
A Modern JavaScript Date Library
Length.js
📏 JavaScript library for length units conversion.
Selectivizr
Selectivizr is a JavaScript utility that emulates CSS3 pseudo-classes and attribute selectors in Internet Explorer 6-8.
Hitch
A lightweight engine that allows you to hitch new capabilities to the browser (prollyfill).
Css3 Finalize
Tired of adding prefix for each broswer when it comes to the new css3 attributes?
HTML5shiv
This script is the defacto way to enable use of HTML5 sectioning elements in legacy Internet Explorer.