Event-based communication models provide interesting properties for distributed systems such as asyn hronism and type-based selection mechanisms.The Comet middleware we develop proposes such an event-based communication model as foundation.From this canonical model, we show how to build more conventional bidirectional and synchronous interactions with extended features such as impli it type-based multi ast or asynchronous perationalization. Furthermore,we demonstrate the use (and interest)of the lower-level asynchronous model to develop highly flexible distributed services.We illustrate this idea with a publish/subscribe protocol that can be dynamically reconfigured to match various requirements:type-based or content-based filtering semantics, peer-to-peer or mediator-based configurations.