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 code-based diagramming tool favored by developers for its flexibility and customizability, while Gliffy is a user-friendly diagramming application that excels in collaboration and template options. The choice between them depends on the user's technical proficiency and specific diagramming needs.