In Ambient Intelligence environments machines proactively and transparently work on behalf of humans. The nature of these machines and the communication protocols they use is multifarious. Therefore, the applications running on top of them remarkably demand interoperability. The Triple Space Computing (TSC) paradigm addresses that problem by sharing information represented in a semantic format through a common virtual space. As long as application developers use standard ontologies, different applications using the same spaces will interact automatically. The focus of this paper is to present Otsopack, a fully distributed TSC middleware designed to meet the needs of mobile and resource constrained devices. Otsopack defines a simple HTTP interface for the TSC operations. This interface focuses on simplicity and modularity, so that two implementations that support different modules can still interact. To assess the middleware we provide time and load measurements, and we analyze two independent implementations.