CodePen is a playground for the front-end side of the web

JS Bin is another playground and code-sharing site of front-end web (HTML, CSS, and JavaScript. It Also supports Markdown, Jade, and Sass)

Coding Assistant that lets you search, define, and reuse code snippets directly in your IDE. Free for individual and small organizations

Visual Studio Code for CS50 is a web app at code.cs50.io that adapts GitHub Codespaces for students and teachers

Online Playground for React, Vue, Angular, Preact, and more

Code snippet organizer with labels and support for 100+ programming languages

Quantified self-metrics about your coding activity using text editor plugins, limited plan for free

Spring Boot app generator with custom database and REST API