Mimosa
A lightning-fast, modular, next generation browser development tool.
Nightwatch
UI automated testing framework based on node.js and selenium webdriver
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.
Roughdraft.js
Quickly create an interactive HTML mock-up by auto sourcing lorem ipsum/images generators, with minimal html markup, and no server side code
Monitor.io
remote monitoring and debugging for socket.io
Spa Eye
Backbone debugger for Firefox
Apitizer
API mocking for client JavaScript applications
Angular Debaser
Just a better way to test AngularJS apps.
Jscritic
Quickly check how well 3rd party script behaves.
Thrill
Runs tests in many browsers.