Scoop - A command-line installer for Windows
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.
Windows Remix - Web-based batch software installer with zero dependencies. Recommended first visit after reinstalling Windows or buying a new laptop.
Ruby Toolbox - Explore and compare open source Ruby libraries
Aiiguide - Aiiguide is a library of more than 200,000 applications that you can download and install on Windows and macOS.
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.