Description: Codapi is a platform for embedding interactive code snippets directly into your product documentation, online course or blog post.
Codapi manages sandboxes (isolated execution environments) and provides an API to execute code in these sandboxes. It also provides a JavaScript widget codapi-js for easier integration.

Source: https://github.com/nalgeon/codapi

Description: A website for writing and running scripts in the browser, including versioning, an API, scheduling and more.

Description: The most fun place to experiment with layouts using variable fonts, and export front-end code right from this little web app. Designed and developed by Wenting Zhang.

Description: PHP Sandbox is an online code sandbox for PHP that makes prototyping and sharing of PHP projects swift and painless!

Description: Thimble. Mozilla is a global nonprofit dedicated to keeping the Internet a global public resource that is open and accessible to all.

Description: Discover gists. GitHub Gist: instantly share code, notes, and snippets.

Description: dabblet.com. An interactive CSS playground and code sharing tool. Dabblet saves to Github gists and offers many conveniences for CSS editing.

Description: JS Bin. Sample of the bin:

Description: An online code editor, learning environment, and community for front-end web development using HTML, CSS and JavaScript code snippets, projects, and web applications.

Description: JSFiddle - Code Playground. Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.