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.
Alternato - NOTE: Not available in English.
Product Hunt - A website that lets users share and discover new products
Aventrix - Aventrix is a website that helps you discover new and fun activities.
Alternative.me - Welcome to alternative.me, the source of better software alternatives. Finding suitable software was never easier.
Slant.co - Slant is a collaboratively edited resource that helps you quickly make decisions.