ApexSQL Monitor - SQL Server performance monitor - Monitor, detect, and solve SQL Server performance problems on any device
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.
dbForge Monitor - dbForge Monitor is a FREE add-in for Microsoft SQL Server Management Studio that allows you to track and analyse SQL server performance.
RedGate SQL Monitor - SQL Monitor helps you and your team find issues – before they become problems
Visual Expert - An all-in-one Static Code Analysis + SAST tool for PowerBuilder, Oracle and SQL Server
SQL Sentry - SentryOne is the most capable, scalable software for data DevOps and database performance monitoring.