RedGate SQL Monitor - SQL Monitor helps you and your team find issues – before they become problems
Zabbix - Track, record, alert and visualize performance and availability of IT resources
SQL Sentry - SentryOne is the most capable, scalable software for data DevOps and database performance monitoring.
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.
Idera - IDERA offers powerful software to help data and IT pros work smarter not harder. See what IT and database management tools will make your job easier and better.
Prometheus - An open-source systems monitoring and alerting toolkit.