Chromeless - Headless Chrome automation on AWS Lambda
browserling - Live interactive cross-browser testing from your browser.
jsdom - A JavaScript implementation of various web standards, for use with Node.js - jsdom/jsdom
BrowserStack - BrowserStack is a software testing platform for developers to comprehensively test websites and mobile applications for quality.
Selenium - Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that.
Browsershots - Browsershots makes screenshots of your web design in different browsers.