Jungle Scout - Amazon product research made easy.
File-Extensions.org - Large computer file extension library with detailed explanation of each file type with links to download free or associated software programs.
Inventory Spy - Spy how many products remain on any Amazon Product’s offer listing page.
FileProInfo - It's All About Files, Software, Online Tools - 100% Free
AMZScout - AMZScout extension will help you make a decision about picking a niche based on the actual data, not intuition.
GroupDocs - GroupDocs is a web-based service for online document sharing, collaboration and management.