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.

Refined GitHub - Browser extension that makes GitHub cleaner & more powerful

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.

GitZip - Download or create a download link for a GitHub project folder/sub-folder or file.

JSter - JSter is a community-driven catalog of the most useful javascript libraries.

Board for Github - A webview based GitHub project app with native features