Working on ScreenWall (https://www.screenwall.app) because I had old phones sitting in a drawer doing nothing, and now I use them as passive widgets on my desk and wall. I use the browsers of the devices to join a shared "wall". From there I can push images, video, gifs, or a synced canvas to it (and any other old screens I add) without installing anything. Started as a one-device hack for my desk clock, but it scales to syncing multiple screens at once if you've got more than one old device lying around.