Ontopia is a set of tools for building applications driven by Topic Maps, such as Web portals. The main benefit of Topic Maps is that they provide a flexible and expressive data model supporting much better findability than traditional solutions, as well as advanced features like automated merging of datasets.
The Ontopia company (http://www.ontopia.net/) released a new first version of the open source Ontopia toolkit (called Ontopia 5.0.0), which is built based on the same product as the old commercial Ontopia Knowledge Suite, but with an open source license, and with the old license key restrictions removed. The new version has been created by both the Ontopia team who has always worked on the product, but also by open source volunteers.
Tools from this suite have been successfully used by FAO partners such as the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT, Ref.: Balaji, V [V.Balaji@CGIAR.ORG]) in the agricultural domain. An example is available at http://test2.icrisat.org/.
Download the tool from: http://code.google.com/p/ontopia/downloads/list