ManageEngine M365 Manager Plus - Auditing, monitoring and reporting tool for Office 365
Zabbix - Track, record, alert and visualize performance and availability of IT resources
DareBoost - DareBoost is an online tool to test, analyze and monitor your website: speed, SEO, quality, security. All you need for website optimization in a single service.
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.
AppSignal - We monitor the software that makes your customers happy.
Prometheus - An open-source systems monitoring and alerting toolkit.