BigTracker is described as 'focuses on finding a product niche and competitors analysis with more accurate data. BigTracker currently works for the US, UK, and JP marketplaces. The more marketplaces like DE will soon be available in Q1, 2018'. There are nine alternatives to BigTracker for a variety of platforms, including Online / Web-based, Mac, Windows, Linux and Google Chrome. The best alternative is Jungle Scout. It's not free, so if you're looking for a free alternative, you could try Egrow or Upwin club. Other great apps like BigTracker are AmzScope (Paid), AMZScout (Paid), Sellics (Paid) and Unicorn Smasher (Paid).
AmzChart is an Amazon product research and BSR chart tool. BSR stands for best sellers rank and it's a ranking that Amazon gives to the products based on a number of factors such as rating and reviews, sales velocity, and other methods that they never disclosed publicly.