StarUML

StarUML is a fully fledged, open source, UML modeling tool that supports the ability to create software designs, from basic concepts, through to the coded solution.

Users should beware that this tool is more complex than a simple UML diagram editing tool, in that, through the use of the Model Drive Architecture (MDA) standard, the tool supports complex modeling which is realizable in code.
The package is aimed at the serious developer and is not suitable for beginners. Once the tool is mastered, the user can produce professional results without the need to invest in more costly commercial tools such as Borland Together or Rational Rose, which perform the same function.
The tool supports the ability to add plug-ins to the basic system. Although written in the Delphi language, these plug-ins can be written in any COM-compatible language, such as C++, Delphi, C# and VB.
On completion of the software design, represented as a model set, the Diagram Overview mode allows the user to see an at-a-glance view of the overall solution before completion.
For the creation of professional UML models with the follow through capability of creating the coded solution, this package is hard to beat unless you are willing to pay for a commercial tool. However, this is not a tool aimed at the beginner who is just getting to grips with UML, although it is probably the most user-friendly introduction for those who need to understand the full weight of UML based development techniques. It is unfortunate that this tool is currently inactive in terms of the development of new releases. Nevertheless, anyone who needs exposure to UML concepts, especially to assist in understanding the difference between a software diagram, the underlying model, and the different views of that model, then this tool fits that purpose.