User-centered consultation systems can be viewed as systems with trust in the competence of the user, whereas conventional knowledge systems are often based on some mistrust. By offering a variety of formal and informal diagnostic services mediated by flexible agents, the user solves his or her problem by asking the agents for specific information complementary to his or her knowledge. The development process is flexible enough to build minimalist Wiki-like informal systems very quickly, which can be incrementally refined and formalized in a distributed manner. The approach is demonstrated with two case studies. Categories and Subject Descriptors I.2.1 Applications and Expert Systems, I.2.11 Distributed Artificial Intelligence, H.3.3 Information Search and Retrieval, Retrieval Models General Terms Design, Management Keywords Consultation system, diagnosis, agents, Wiki-systems, knowledge-based systems, distributed knowledge acquisition.