Wikidata went live two years ago, but the II in the title is also a reference to the first page called Wikidata on meta.wikimedia.org which for years collected ideas for first class data support in Wikipedia. I had linked to Wikidata I writing about the most prominent of those ideas, Semantic MediaWiki (SMW), which I later (8 years ago) called the most important software project and said would “turn the universal encyclopedia into the universal database while simultaneously improving the quality of the encyclopedia.”
SMW was and is very interesting and useful on some wikis, but turned out to be not revolutionary (the bigger story is wikis turned out to be not revolutionary, or only revolutionary on a small scale, except for Wikipedia) and not quite a fit for Wikipedia and its sibling projects. While I’d temper “most” and “universal” now (and should have 8 years ago), the actual Wikidata project (created by many of the same people who created SMW) is rapidly fulfilling general wikidata hopes.
One “improving the encyclopedia” hope that Wikidata will substantially deliver on over the next couple years and that I only recently realized the importance of is increasing trans-linguistic collaboration and availability of the sum of knowledge in many languages — when facts are embedded in free text, adding, correcting, and making available facts happens on a one-language-at-a-time basis. When facts about a topic are in Wikidata, they can be exposed in every language so long as labels are translated, even if on many topics nothing has ever been written about in nor translated into many languages. Reasonator is a great demonstrator.
Happy 2nd to all Wikidatians and Wikidata, by far the most important project for realizing Wikimedia’s vision. You can and should edit the data and edit and translate the schema. Browse Wikidata WikiProjects to find others working to describe topics of interest to you. I imagine some readers of this blog might be interested in WikiProjects Source MetaData (for citations) and Structured Data for Commons (the media repository).
For folks concerned about intellectual parasites, Wikidata has done the right thing — all data dedicated to the public domain with CC0.