Networks are more and more composed of heterogeneous devices that are intermittently connected. Intermittences are induced by the mobility of devices communicating through short-range wireless interfaces, and by the sleep phases made by devices for energy saving purposes. Discovering, invoking and compositing services in such networks can therefore be difficult tasks. This paper presents a middleware system to achieve these tasks efficiently, thanks to opportunistic networking and computing techniques that are designed to minimize the execution time of these tasks, as well as to maximize their success ratio.