[alextgordon]

Could really do with having private hidden rooms, so I can play with a few friends without having the whole world barge in.

[jaredsohn]

You can do this. In the bottom left you can choose among existing rooms or create your own. If you create your own room, you have the option of making it private/hidden (although it seems like it becomes public whenever the server is reset.)

You can also instantly create your own room by adding /[roomname] to the url (although I don't know if this makes them public or private.)