I was travelling recently with a group of people and wondered whether something like this might exist. My use case was to have a way of easily sharing photos with people close by (we were all being driven around in the same car) without the need to involve anything dodgy like Facebook. WiFi did cross my mind as we were all connected via the same pocket WiFi adapter although I was wondering if it could be made to work without an internet connection. Especially useful when you're travelling through regions with patchy cell coverage.