Codacy - Automatically reviews code style, security, duplication, complexity, and coverage on every change while tracking code quality throughout your sprints.
GitHub Visualizer - Enter user/repo and see the project visually
Refactor.io - Share your code instantly for refactoring and code review
GHuser - Better GitHub profiles for everyone
CodeStream - CodeStream helps development teams resolve issues faster, and improve code quality by streamlining code reviews inside your IDE
Octohunt - Search to find developers in your city on Github.