GitNews Web - Trending repositories from GitHub, HackerNews & Reddit
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.
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.
SimilarSites - Easily find more sites like those you like.
Ruby Toolbox - Explore and compare open source Ruby libraries
Product Hunt - A website that lets users share and discover new products