• CodePen - HTML/CSS/JS. Choose from pre-processors e.g. pug and markdown and HTML, Less and SCSS for CSS and TypeScript or Babel for JS.
  • JSFiddle - HTML/CSS/JS. Choose from JS libraries.
  • Fiddles - Links to fiddle sites
  • SoloLearn code playground - Pick a language from the droplist. HTML/CSS/JS, C, Python 3 and more. SoloLearn has online courses, code challenges and community which creates and shares their code.
  • REPL - click “new repl” from the homepage or explore available languages on the languages page.

You might find an article like this useful, as it compares them in more detail. hongkiat.com - Coding Playgrounds