In this paper, we present Mist: a reliable and delay-tolerant middleware for information dissemination between highly mobile devices. Mist provides publish/subscribe with guaranteed message delivery in fully connected networks. Through emulation we show how the middleware is effective in static networks, as well as in dynamic topologies with high mobility. We describe how Mist is able to scale using a topic routing mechanism, allowing groups of mobile units to cooperate with infrastructure-based P2P-networks. Finally, we describe recent experiments where Mist has been employed successfully in real-life deployments. The implementation of the middleware, written in Java, is released as open source.