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.
Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
UptimeRobot - Free Website Uptime Monitoring
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Codeship - Codeship is a fast and secure hosted Continuous Delivery platform that scales with your needs.