Gitstalk - Discover what your favorite GitHub users are up to
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
AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.
GitNews Web - Trending repositories from GitHub, HackerNews & Reddit
GitSpo - Measure & engage your open-source community