Quick Diagram - A tool for generating diagrams and flowcharts from text.
draw.io - Online diagramming application
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.
FYI - Find your documents, like magic 🔮
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Superdocu - Onboard people at scale, stay compliant.