A completely equivalent alternative, that's ready to use "out of the box"? Probably not. But a lot of the pieces you need to build something like Google's knowledge graph are out there.<p>For starters, you have things like Wikidata[1] and dbPedia[2] which give you access to Wikipedia data in a structured form. Then you have datasets like OpenCyc[3] and Freebase[4] that you could include.<p>Then, there are tools like Stanbol[5] which can, to a certain extent, extract structured data from free text. Of course this isn't perfect, since you'd basically need to have solved AGI to do this completely. But you can get <i>some</i> "knowledge" from free text. Combine that with a crawling system like ManifoldCF[6] or Nutch[7] or something, and you could imagine building a pipeline to crawl websites and add to your knowledge-base.<p>If you decide to use RDF as the representation for the knowledgebase, there are things like Jena[8] that let you store and query your KB and do inference against it. Do all that, and probably add in a little more AI / NLP and you can build your own knowledge graph.<p>OK, yes, the "add a little more AI" bit is kinda hand-wavy, but that's an area of open research. Still, there are practical things that can be done today... and if you're looking for a thesis topic, well, here ya go. :-)<p>[1]: <a href="https://www.wikidata.org/wiki/Wikidata:Main_Page" rel="nofollow">https://www.wikidata.org/wiki/Wikidata:Main_Page</a><p>[2]: <a href="http://wiki.dbpedia.org/" rel="nofollow">http://wiki.dbpedia.org/</a><p>[3]: <a href="http://sw.opencyc.org/" rel="nofollow">http://sw.opencyc.org/</a><p>[4]: <a href="https://developers.google.com/freebase/" rel="nofollow">https://developers.google.com/freebase/</a><p>[5]: <a href="http://stanbol.apache.org" rel="nofollow">http://stanbol.apache.org</a><p>[6]: <a href="http://manifoldcf.apache.org" rel="nofollow">http://manifoldcf.apache.org</a><p>[7]: <a href="http://nutch.apache.org" rel="nofollow">http://nutch.apache.org</a><p>[8]: <a href="http://jena.apache.org" rel="nofollow">http://jena.apache.org</a>
@mindcrime has put a pretty extensive list and explanation.<p>The things is, you are probably looking for a solution that does the reconciliation of data arriving from multiple sources and formats for you and preferably exposes it over an easy to use API.<p>You can try <a href="http://unigraph.io" rel="nofollow">http://unigraph.io</a>, the API Sandbox (GraphQL) is available at: <a href="http://u01.unigraph.rocks" rel="nofollow">http://u01.unigraph.rocks</a> and an extensive documentation covers it at: <a href="https://github.com/unigraph/docs/wiki" rel="nofollow">https://github.com/unigraph/docs/wiki</a><p>Currently Unigraph combines data from:<p>- wikidata<p>- geonames<p>- freebase<p>- crunchbase<p>- SEC EDGAR<p>- Companies House (UK).<p>A datadump is on its way and more sources will be added soon.<p>Disclaimer: I am building Unigraph, precisely for the reason of the question: "An open alternative to GKG".
There would be, of course, one (if not the no. 1) google knowledge graph source: Wikidata.<p><a href="https://www.wikidata.org/wiki/Wikidata:Main_Page" rel="nofollow">https://www.wikidata.org/wiki/Wikidata:Main_Page</a>