In this paper we present the Nexus Platform for context-aware applications. This platform allows to share the effort of setting up a global and detailed context model between different providers by federating their partial models. Applications can query data directly, use push-based communication through an event service, or use value-added services like a navigation or map service for special tasks. Additional context-aware services like hoarding or geocast can be implemented on basis of the platform. For the latter we present different approaches for addressing and efficient message forwarding based on the Nexus Platform.