I was just experimenting on how to make a cloud game for multiplayer. You can go on the project, and if anyone else is viewing the project from another device, you will be able to see them controlling their player!
This is not a game yet. It is just a test to see if I can make a cloud server. If you are a "new scratcher", this will not work. If you are, then you will be getting a notification from scratch saying something like, "This project uses cloud variables, which are only avalible to official scratchers". The notification will appear on the project page before you click the green flag.