Internet pervasive services call for flexible supports to enable a wide degree of collaboration. On the one hand, many people are connected to the Internet and surf the Web not only to retrieve information, but also to carry out several kinds of different tasks via the on-line services. On the other hand, the Internet is likely to be soon populated by software agents that will act in behalf of users, “intelligent” enough to achieve the better result without boring their users. In this paper we present a Web-based modular architecture that permits interaction and collaboration among people and agents, leading to a more fruitful exploitation of the capabilities offered by the Internet. A negotiation application based on auctions is used to show the advantages of the proposed architecture.