Firefly UML
A free, easy-to-use and user-friendly Java-based UML editor.
...With class diagrams, sequence and instance diagrams, Firefly UML provides a solid selection from the vast range of existing UML diagram types.
Firefly UML is really easy to learn as it provides you multiple ways of access to the same function - be it mouse action, hotkey, context menu or toolbar icon. And the best thing is: once you have learned how to handle one type of diagram, you also have learned how to deal with the other diagram types, because they all follow the exactly same user interaction patterns.
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