freeCodeCamp alternatives to codepen due to:

freeCodeCamp alternatives to codepen due to:“You need a valid referrer to Log In to CodePen”

This link explains clearly why this happens:

For the Responsive Web Design Projects we must use, we get a message like this: “For now, the test suite only works in Chrome! Please read the README below in the JS Editor before beginning.” which I likely doubts is strictly related to this issue as I could have Chrome and yet still have a Refferer controler.

Are there any possibilities to have other playgrounds rather than in the future?

You use,, Also, you could host the project on your own website as long as the written source code is available somewhere (i.e. GitHub).