draw.io - Online diagramming application
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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.
AppZero - AppZero is a monitoring and migration tool that allows users to keep track of different applications and servers in both simple and complex IT environments.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
RedGate SQL Monitor - SQL Monitor helps you and your team find issues – before they become problems