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.
Productz.com - Crowdsourced products database
Top Best Alternatives - Search and choose the right software alternative with our crowdsourced software recommendation engine.
Versus - Find popular alternatives to anything in a jiffy
Capterra - Capterra helps millions of people find the best business software. With software reviews, ratings, infographics, and the most comprehensive list of the top business software products available, you're sure to find what you need at Capterra.
Diffen - Compare anything to find similarities and differences. Read, improve or create comparisons.