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.

OctoSearch - Search the repositories starred by your following on 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.

GitHub Visualizer - Enter user/repo and see the project visually

GitNews Web - Trending repositories from GitHub, HackerNews & Reddit

Gource - Gource is a software version control visualization tool.