From the webpage:
Wikidata is a free knowledge base that can be read and edited by humans and machines alike. It is for data what Wikimedia Commons is for media files: it centralizes access and management of structured data, such as interwiki references and statistical information. Wikidata contains data in all languages for which there are Wikimedia projects.
Not fully operational but still quite interesting.
Particularly the re-use of information aspects.
Re-use of data being one advantage commonly found in topic maps.