Thimble is “a code editor, web server, web browser & developer tools all in one—and it’s free.” Learn or teach HTML, CSS and JavaScript and quickly create and publish web pages.
Thimble includes many useful features including: Instantly see your changes, remix any Thimble project, handy code snippets, built-in JavaScript console, add and manage files, turn the lights on and off, follow and create embedded tutorials, get code hints as you type, edit CSS right in your HTML pages, publish projects to the web fast, pick colors right in the editor, test your project on a mobile device, find HTML elements fast, image filters and take a selfie.