In my opinion, the magic here is the `window.screen[XY]`, not the communication method, which could be anything. As others have mentioned, you can do this with

In my opinion, the magic here is the `window.screen[XY]`, not the communication method, which could be anything. As others have mentioned, you can do this with localStorage, websockets or even Cookies. The novelty is that each window knows its size and location (through `window.*`) and renders something interesting. I was a bit surprised to see that the browser gives information of where the window is in the window manager as I would have guessed that to be privileged information and a potential security issue, but what do I know.