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.

Ruby Toolbox - Explore and compare open source Ruby libraries

Top Similar Sites - Top Similar Sites helps you find similar, alternative or related sites to any website instantly.

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.

Growing Page - Browse web projects and evaluate them by multiple criteria.

Libre Projects - A directory of free & open source hosted web applications and alternatives to many proprietary...