I got this wonderful free tool which is free for download and ofcourse it's OpenSource. Although I have not gone through all the functionalities of this tool but I'll be exploring it very soon.
What is StarUML?
StarUML is an open source project to develop fast, flexible, extensible, featureful, and freely-available UML/MDA platform running on Win32 platform. The goal of the StarUML project is to build a software modeling tool and also platform that is a compelling replacement of commercial modeling tools such as Rational Rose, Together and so on.
Key Features
- UML 2.0 diagrams
- Various language support. (Java, C++, C# modules)
- Microsoft Office documents (Word, Excel, and PowerPoint) generation based on customizable template.
- Customizable code generation.
- Support MDA technology. (UML profiles and customizable diagrams)
- Diagram extensibility. (Define your own type of diagram beyond the UML)
- High compatibility. (Rose, XMI modules)
- Model verification (based on UML 1.4 well-formedness rules)
- Pattern support
Screenshot
Links:
http://www.staruml.com/
http://staruml.tigris.org/
It's really a great free tool, explore it in your spare time !