Coverity Scan - Find and fix defects in your Java, C/C++ or C# open source project for free
Watchtower - "Watchtower monitors your competition's websites and alerts you to important changes instantly."
SonarQube - SonarQube, a core component of the Sonar solution, is an open source, self-managed tool that systematically helps developers and organizations deliver Clean Code.
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
ReSharper - ReSharper is a productivity tool for visual studio that provides tools and features to help you manage your code.
Material Design for Bootstrap 4 - Powerful and free UI KIT for the newest Bootstrap 4 and Material Design