When migrating applications between devices during runtime, one has achieved application mobility. In this paper we present the XAM system, providing application mobility through a peer-to-peer based solution over heterogeneous networks. Our architecture takes into consideration established requirements of application mobility, being application identification and distribution; context-awareness and context quality; seamlessness; heterogeneity support; and usability. Our system differs from traditional systems as it provides application mobility in a decentralized manner over heterogeneous networks, using different communication technologies. Following the evaluation of our system, we also discuss major challenges and possibilities for the continuing evolution of application mobility systems.