We present an architecture supporting ad-hoc composition of pervasive services, an open-source framework that implements it, and the key design principles behind it. The architecture focuses on direct human interaction, supporting combination of devices and services that are not explicitly designed to work together. The focus is on local networks, but extension is possible to wide area networks, interconnecting several local networks. The information about how services are connected and coordinated is collected in a new construct called assemblies. Separating this information from the services themselves allows combination of existing services in new creative ways without changing them.
Assemblies can provide new services and in this way be organized hierarchically. The assembly makes the architecture of a pervasive system explicit, providing an overview understandable to users. Discovery and connections across different network technologies is supported. The architecture has been used for  applications in large scale networks, and offers mechanisms useful for system integration in general.

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