App Annie - App Annie is a marketing analytics tool available for apps of all kinds. With App Annie, you can track sales, traffic, and a variety of other factors pertinent to monitoring an app's trajectory.
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.
AppFollow - AppFollow is an integrated solution that makes monitoring, analyzing, and elevating your app's reputation easy.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
appfigures - Cross-platform app store analytics for all of your mobile apps.
Better Uptime - We call you when your website goes down