Skuuudle - Discover, match and monitor your eCommerce competitors.
Watchtower - "Watchtower monitors your competition's websites and alerts you to important changes instantly."
Price2Spy - Price2Spy is a price monitoring, pricing analytics, and repricing tool, meant to help eCommerce professionals keep an eye on their competitors or retailers.
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
BuiltWith - Find out the technology behind websites
Material Design for Bootstrap 4 - Powerful and free UI KIT for the newest Bootstrap 4 and Material Design