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.
GitSheet - A dead simple Git cheat sheet.
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.
AI Cheatsheet - A tool to help you ace AI basics
GitSpo - Measure & engage your open-source community
Code House - A whole new world of 300+ developer cheat-sheets