Code Climate for Google Chrome - Code quality and test coverage, directly in GitHub
GitHub Visualizer - Enter user/repo and see the project visually
Devo - Devo delivers real-time operational & business value from analytics on streaming and historical data to operations.
Github Profile Visualizer - Tool for visualizing GitHub profiles
Git Random - Chrome extension to replace new tab with random github user
The GitHub Matrix Screensaver - Latest commits from GitHub visualized Matrix-style