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.
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.
RedGate SQL Monitor - SQL Monitor helps you and your team find issues – before they become problems
UptimeRobot - Free Website Uptime Monitoring
SQL Sentry - SentryOne is the most capable, scalable software for data DevOps and database performance monitoring.
Zabbix - Track, record, alert and visualize performance and availability of IT resources