StatusGator - Monitor all your hosted applications, vendors, and websites, and keep your team informed of outages. StatusGator is the world's premier status aggregator, status page, and website monitoring tool.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Amazon CloudWatch - Amazon CloudWatch is a monitoring service for AWS cloud resources and the applications you run on AWS.
IsDown App - Monitor all your cloud services status pages in one place
DeployBot - Push. Build. Deploy! Instantly build and ship code anywhere in one consistent process for your entire team.
DigitalOcean Monitoring - Collect metrics, monitor Droplet performance, and receive alerts when problems arise in your infrastructure—no configuration required.