Sauce Labs - Test mobile or web apps instantly across 700+ browser/OS/device platform combinations - without infrastructure setup.
WebGazer.js - Eye tracking on the browser
LambdaTest - Perform Web Testing on 2000+ Browsers & OS
BrowserStack - BrowserStack is a software testing platform for developers to comprehensively test websites and mobile applications for quality.
Browserless - Headless browser automation built for developers.
CodePen - A front end web development playground.