CodePen - A front end web development playground.
Pinegrow - A professional visual editor for Bootstrap 4 and 3, Foundation, responsive design, HTML, and CSS. Convert HTML to WordPress themes.
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
BlueGriffon - An HTML editor based on Mozilla rendering engine.
JS Bin - Sample of the bin:
Webflow - Build dynamic, responsive websites in your browser. Launch with a click. Or export your squeaky-clean code to host wherever you'd like. Discover the professional website builder made for designers.