Git analytics - for software developers, teams, and open-source communities
Ruby Toolbox - Explore and compare open source Ruby libraries
Good First Issue - Make your first open-source contribution
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.
GitSheet - A dead simple Git cheat sheet.
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.