In this paper we present a generic framework for developing complex distributed applications in open information environments, using reactive agents as basic building blocks. We address agent architecture and collaboration issues by introducing a minimal agent architecture, the Reactive Information Agent, and adopting a flexible asynchronous communication infrastructure, the Inter-Agent Communication Model. Finally, we present an implementation of the framework which allows agent designers to rapidly develop multi-agent systems based on simple heterogeneous computational elements, which are mobile, adaptive, reflective, and dynamically reconfigurable during the system lifetime.