UMLet For Mac

UMLet is an open-source UML tool with a simple user interface: draw UML diagrams fast, export diagrams to eps, pdf, jpg, svg, and clipboard, share diagrams using Eclipse, and create new, custom UML elements.

UMLet is a UML tool aimed at providing a fast way of creating UML diagrams. UML elements are modified using text input instead of pop-up dialogs. Elements can be modified and used as templates; this way, users can easily tailor UMLet to their modeling needs.

UMLet supports a variety of UML diagram types: class diagrams, use case diagrams, sequence diagrams, state diagrams, deployment diagrams, activity diagrams -- see some examples.

UMLet allows users to create their own custom UML elements. An element's look can be modified at run-time by changing a few lines of Java code; UMLet then compiles the new element's code on the fly. Without leaving UMLet, users can thus create and add new element types to their diagrams.

UMLet's design goals are also described in this paper and this one. The custom elements' concept is described here. Another simple UML tool is Violet.