B.S. Detector is described as 'browser extension that warns users about unreliable news sources. It basically searches all links on a given webpage for references to unreliable sources, checking against a manually compiled list of domains'. There are three alternatives to B.S. Detector for Google Chrome, Linux, Mac and Windows. The best alternative is Fake News Monitor, which is free. Other great apps like B.S. Detector are StB (Free, Open Source) and FiB (Free, Open Source).
The FiB Chrome extension analyzes your Facebook feed for a url, picture, and text's validity. It was built by four students as part of Princeton University's hackathon, with the challenge to solve Facebook's problem with fake news.