PlantUML is an open-source tool allowing users to create UML diagrams from a plain text language. Developed by Arnaud Roques
License: Open Source
PlantUML is a powerful open-source tool primarily focused on UML diagrams with a text-based approach, while ThinkComposer is more user-friendly and suited for brainstorming and conceptual modeling with a collaborative platform. PlantUML caters to developers needing version control, while ThinkComposer serves those looking for an intuitive diagramming experience.