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 an open-source tool focused on text-based diagram creation, making it ideal for developers and technical users, while SmartDraw offers a more user-friendly graphical interface suitable for business professionals. The choice between them largely depends on user preference for coding vs. visual design.