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.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Product Hunt - A website that lets users share and discover new products
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Slant.co - Slant is a collaboratively edited resource that helps you quickly make decisions.
Better Uptime - We call you when your website goes down