The TM4J project is an open source project with contributors from around the world. The current focus of the TM4J project is on the development of a topic map "engine" which processes files conforming to the XML Topic Maps (XTM) specification and stores them either in memory or in a persistent store, providing access via a Java API. Future development plans include a framework for developing web applications using topic maps and a navigation/editing application for topic maps.

http://tm4j.org/

The goal of the TM4J project is to provide a suite of topic map processing libraries and tools.