Computers have become affordable, small, omnipresent and are often connected to the Internet. However, despite the availability of such rich environment, user interfaces have not been adapted to fully leverage its potential. To help with complex tasks, a new type of software is needed to provide more user-centric systems that act as ”intelligent assistants”, able to interact naturally with human users and with the information environment. Building an intelligent assistant is a difficult task that requires expertise in many fields ranging from artificial intelligence to core software and hardware engineering. We believe that providing a unified tool and methodology to create intelligent software will bring many benefits to this area of research. Our solution, the Active framework, combines an innovative production rule engine with communities of services to model and implement intelligent assistants. In the medical field, our approach is used to build an operating room assistant. Using natural modalities such as speech recognition and hand gestures, it enables surgeons to interact with computer based equipments of the operating room as if they were ac tive members of the team. In a broader context, Active aims to ease the development of intelligent software by making required technologies more accessible.