Commodity Wi-Fi based device-free localization has attracted a great attention in recent years. Previous related work is either fingerprint-based or model-based. In this demo, we will demonstrate a generic Fresnel Penetration Model (FPM) based real-time device-free localization system called MFDL. Using only three to four commodity Wi-Fi devices, it can localize a metal plate reflector with 6cm median error in the open space and localize a moving person with 45cm median error in an outdoor space of 36m² and 50-75cm median error in indoor environments with a size ranging from 25m² to 72m², outperforming the state-of-the-art device-free localization approaches in similar settings.