Ruby Toolbox - Explore and compare open source Ruby libraries
Product Comparisons - Compare any 2 software products
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.
Insider Company Comparisons - Compare hundreds of top tech companies all in one place
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.
Startup Stash - A curated directory of 400 resources & tools for startups