https://github.com/EbookFoundation/free-programming-books/blob/master/free-programming-playgrounds.md

SQL

• Extends Class
• SQLFiddle

CSharp/.Net

• https://repl.it/languages/csharp
• https://dotnetfiddle.net/

Typescript

• https://stackblitz.com/edit/typescript-3s5atn

JavaScript

• https://stackblitz.com/edit/js
• https://scotch.io/tutorials/7-javascript-playgrounds-to-use-in-2019
• https://github.com/EbookFoundation/free-programming-books/blob/master/free-programming-playgrounds.md#javascript
• https://playcode.io/
• CodePen
• CodeSandbox.io (React)
• JSBin
• JSFiddle
• Plunker
• Sololearn

React

• https://stackblitz.com/edit/react-teuhff
• https://codesandbox.io/s/reactbasic-emxuz

Node/Express

• https://repl.it/languages/express