SOFA " The SOFA (Simple Ontology Framework API) is a Java API for modeling ontologies with Java language. It integrates ontology engineering tasks with the Java programming by providing an object model of an abstract, language-neutral ontology for Semantic Web applications, Knowledge Bases and other ontology-driven software."
Seems similar in initial concept to the WonderWeb Ontology API. However, it's much simpler with the 4 basic concepts of: Ontology, Thing, Concept and Relation. It seems to sit on top of Jena though, unlike WonderWeb's.