GitSpo - Measure & engage your open-source community
Refined GitHub - Browser extension that makes GitHub cleaner & more powerful
Devo - Devo delivers real-time operational & business value from analytics on streaming and historical data to operations.
List.community - Easy way to browse curated lists on GitHub
LibHunt - LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular projects and their alternatives.
Octoview - The missing preview feature for GitHub