Cloud variable 'chat room' projects are not allowed on Scratch.

Cloud chat projects use cloud variables to allow Scratchers to have text-based communication with each other. We’ve seen people occasionally make these on Scratch, but Scratchers generally use these projects to try to get around the Community Guidelines. We’ve had a lot of discussions about these projects and we’ve concluded that they just aren’t able to work in a way that is safe and appropriate for Scratch.

FAQ

Will my project with cloud-based chat functionality be removed?
Yes, we will be removing projects with cloud based chat. We would encourage you to un-share it or edit the project to remove the chat functionality on your own.

What do I do if I see a project with cloud chat?
We ask that you please use the report button to let us know.

What if my cloud chat uses a whitelist of acceptable words?
We will be removing all projects we see with cloud-chat functionality, even if they have whitelists.

What do you consider to be a cloud chatroom project?
Any project that allows people to enter free text that can be read by someone else, or provides another means for people to communicate freely through a project.

What if I make a chat project that has other safeguards built in?
If it's still a chat project, it violates this policy.

What about projects that allow people to share emojis with each other, or that use a few pre-made sentences?
These are generally fine as long as they can't be used to share content that the people viewing the project can create themselves.

You can learn more about our Cloud Chat guidelines on this forum post: https://scratch.mit.edu/discuss/topic/357609/