Skuuudle - Discover, match and monitor your eCommerce competitors.
FileProInfo - It's All About Files, Software, Online Tools - 100% Free
Price2Spy - Price2Spy is a price monitoring, pricing analytics, and repricing tool, meant to help eCommerce professionals keep an eye on their competitors or retailers.
File-Extensions.org - Large computer file extension library with detailed explanation of each file type with links to download free or associated software programs.
BuiltWith - Find out the technology behind websites
GroupDocs - GroupDocs is a web-based service for online document sharing, collaboration and management.