Holder
Holder renders image placeholders entirely on the client side.
Rulers Guides.js
Creates Photoshop-like guides and rulers interface on a web page
Nightwatch
UI automated testing framework based on node.js and selenium webdriver
Js Cover
JSCover is a tool that measures code coverage for JavaScript programs.
Bluebird
Bluebird is a full featured promise library with unmatched performance.
Jasmine
DOM-less simple JavaScript testing framework
Trace Kit
Attempts to create stack traces for unhandled JavaScript exceptions in all major browsers.
Angular Debaser
Just a better way to test AngularJS apps.
Blaver
A JavaScript library built on top of the Faker.JS library. It generates massive amounts of fake data in the browser and node.js.
Stacktrace.js
Framework-agnostic, micro-library for getting stack traces in all web browsers
Spa Eye
Backbone debugger for Firefox
Recoil
Recoil is an experimental state management library for React apps. It provides several capabilities that are difficult to achieve with React alone, while being compatible with the newest features of React.
Qunit
An easy-to-use JavaScript Unit Testing framework.
Fast Check
Property based testing framework for JavaScript (like QuickCheck) written in TypeScript
Grunt
Grunt: The JavaScript Task Runner
Browser Sync
Keep multiple browsers & devices in sync when building websites. http://browsersync.io
Csscomb.js
CSS coding style formatter