LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
draw.io - Online diagramming application
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.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Prometheus - An open-source systems monitoring and alerting toolkit.