TM4J is a free topic map engine providing interfaces for the creation, manipulation, import and export of XML topic maps.

Features include:

• An object model which supports all of the constructs of the XTM 1.0 specification
• An extensible command-line utility for determing various statistics for a topic map.
• A command-line utility for merging two or more topic maps automatically.
• An experimental topic map navigation interface using a visualisation from TheBrain.
• An experimental persistent storage back-end which enables processed topic maps to be kept in an Ozone Object-oriented database.

TM4J is open source, hosted at SourceForge, and available under an Apache-style license.