[0] - http://www.sfgate.com/technology/businessinsider/article/It-...
[1] - https://github.com/anantdgoel/HackPrincetonF16
[2] - https://chrome.google.com/webstore/detail/fib/ofpheinlpjdffp...
Such a tool might end up doing a disservice. People arguably already don't think enough about the stuff that's presented to them as facts. I'm not sure outsourcing critical thinking to machines would really help in that respect.
As for the technical aspects, checking multiple sources helps little with regards to the veracity of an article. Many news sites just regurgitate news from other sources or remix previous articles.
If interested, I can help with the back-end. Fullish-er stack person with a few things living in production today (one of which does 500k uniques/month). Ruby/Rails is my go-to. Email is in profile.
Who checks the checkers?