PlantUML

PlantUML is an open-source tool that enables users to create a wide variety of UML and other diagrams using a simple textual language. It supports many diagram types including sequence, use case, class, activity, component, and deployment diagrams, as well as non-UML diagrams like JSON, YAML, and Gantt charts. PlantUML is designed for developers and professionals who prefer text-based diagram creation, offering features like hyperlinks, tooltips, rich text formatting, and multiple layout engines. It runs entirely in the browser and integrates with various tools to streamline diagramming workflows.