Today's mobile devices feature many resources, sensors and data, which make it possible for them to adapt to their environment. However, they would have a lot more resources at hand, and thus could better adapt to their context, if they used their communication capabilities to share their resources with others near them. In this paper we propose the concept of ad-hoc smart spaces, which enables mobile devices to utilize resources owned by other devices in physical proximity. This imposes a number of challenges as cooperation partners can join and leave any time and as devices are highly heterogeneous. We propose a system architecture for ad-hoc smart spaces and present a prototypic implementation.