You are hereVisualizer / Ontopia Project
The Ontopia Knowledge Suite (OKS), including the Ontopia Topic Map Engine, was open sourced by Bouvet in April 2009. It is now known simply as "Ontopia". It was made available by SVN on 16 June 2009 and can probably now be considered the pre-eminent open source topic maps engine.
Bouvet has established Google group and support fora:
A legal structure is currently being finalised.