A really fancy feature that CodeSandbox offers is the ability to import a Github project. If you go to the Create Sandbox page, you'll see some options including Import from Github. From there, paste in the URL to a public github repository and a matter of seconds your entire project will be synced into a new CodeSandbox project.
I recently did this with a create-react-app project and CodeSandbox even knew how to recognize that it was a CRA app so that it could run and display it in the web view.