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.
GitSpo - Measure & engage your open-source community
Product Hunt - A website that lets users share and discover new products
Devo - Devo delivers real-time operational & business value from analytics on streaming and historical data to operations.
Free Software Directory - The Free Software Directory is a project of the Free Software Foundation (FSF) and United Nations...
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.