Monitor and learn SQL Server for free
Open Source SQL Server monitoring framework
Free SQL Server Monitor Power BI Dashboard
 
Simple installation with dbatools

Install-DbaSqlWatch -SqlInstance SQLSERVER1, SQLSERVER2

Multiple installation methods are available, including offline, for those in corporate networks.
Multiple Dashboards
Power BI for in-depth analysis and Grafana for near-real-time screens.

Decentralised and centralised

It collects data on a local instance, and thus it is not restricted by the limitations of the “monitoring” server. In addition, data can be imported into a central repository for easy reporting. SQLWATCH is written entirely in T-SQL so database folks can customise it without having to learn another language.

Custom Actions and Alerts

Actions can send emails, interface with HTTPS endpoints to send PUSH notifications or run arbitrary code.
Send data to Azure Log Monitor
Ease reporting and reduce footprint by offloading data to Azure Log Monitor.