I see that at http://blog.gleam.io/hipchat/ is talked about Public Chat Rooms which I see you can open and participate through a web page, without signing in HipChat, by just choosing your nickname (Full name as they say on the page. Actual chat room is at https://www.hipchat.com/gXGrGMHTO .How can you create a public chat room on HipChat that is publicly accessible?
Public web chat room on HipChat
hipchat
Stuart McKeown helped me out. You have to:Create public chat room.Open Windows clientOpen/Enter the public chat room you have createdClick on bottom right checkbox Guest access is off.  Clicking on it should change it to on. Note that you have to be Admin to be able to allow guest access.