We present the Massive Mobile Multiuser (M³) framework, a platform designed to enable setup-free, real-time, concurrent interaction with shared public displays through large numbers of mobile devices. Simultaneous interaction of multiple persons with public displays requires either dedicated tracking hardware to detect gestures, or a way for users to interact through their personal mobile devices. The latter option provides more flexibility, but also presents a heightened entry barrier as it often requires installation of custom software. To address these issues, M³ enables immediate interaction through the mobile browser without requiring prior setup on the user side, and real-time interaction suitable for fast multiplayer games. We present a live demonstration of our framework at the example of a public game which has already been shown to support up to 17 concurrent users. Despite a resource-constrained environment and an unpredictable selection of client devices, M³ consistently delivers performance suitable for real-time interaction.