browserling - Live interactive cross-browser testing from your browser.
CrossBrowserTesting - Browser Testing made simple! Run automated, visual, and manual tests on 1500+ real browsers and mobile devices. Test more browsers, in less time.
BrowserStack - BrowserStack is a software testing platform for developers to comprehensively test websites and mobile applications for quality.
LambdaTest - Perform Web Testing on 2000+ Browsers & OS
Browsershots - Browsershots makes screenshots of your web design in different browsers.
CodePen - A front end web development playground.