JavaWorld has an interesting article about Protege, An AI tool for the real world:
This article introduces Protégé, arguably the most successful open source knowledge-modeling platform. Using Protégé, developers and domain experts can build conceptual models and knowledge bases and access them via an easy-to-use Java API. The resulting models can implement decision-support systems, capture software requirements, populate databases, generate Java classes and UML diagrams, share and reuse domain models, and access the Semantic Web.
The tool itself appears to really be a rapid prototyping tool that lets you define your data and the relationships between the various parts of it. The more AI-like part of it comes from plug-ins, which includes a plug-in to access the Java Expert System Shell (JESS) and others. I’m going to download this sometime soon (hopefully) and kick the tires a bit.