2 best open source uml tool projects.
StarUML is a software modeling tool to develop fast, flexible, extensible, featureful UML/MDA platform running on Win32 platform. It is a good alternative to Rational Rose. StarUML provides simple and powerful plug-in architecture so anyone can develop plug-in modules in COM-compatible languages.
UMLGraph allows the declarative specification and drawing of UML class and sequence diagrams. The current features are part of an ongoing effort aiming to provide support for all types UML diagrams. Running the UmlGraph doclet on the specification will generate a Graphviz diagram specification that can be automatically processed to create Postscript, GIF, SVG, JPEG, fig, or Framemaker drawings.