Dan Schultz, an MIT graduate now working as a Knight-Mozilla Fellow at the Globe, developed Truth Goggles. It applies about 5,500 fact-checked claims from a database created by PolitiFacts to match information in online content. As you read a story, it presents a colour-coded reading over the particular claim.
Presumably the database will expand as the software develops. Schultz acknowledges there are early limitations to the scale, user interface and detection of paraphrases.