Here’s an interesting open source project, Design Pattern Automation Toolkit. From the web site:

Features

• Allow new design patterns to be plugged into the design of software application as they are discovered. The developers can develop design pattern plug-ins using the application and these design patterns can be merged into the design of a component. Hence it helps in Multi-site development. The design pattern plug-ins are saved in XML format for cross-application portability.
• Allow code generation routines to be plugged into the application for new languages as they emerge. By programming for an interface, the developers can write their custom code generators and create a DLL. These DLLs can be plugged-into the application and used to generate code.
• Allow Reverse Engineering modules to be plugged into the application.  Reverse Engineering helps to understand the structure of an existing software project.
• Provide XML serialization/De-serialization of the projects so that they can be interfaced with other technologies/ languages.
• MetaInfo: The developers can customize the code generation (for ex: final in Java, sealed in C# etc.) by adding the metainfo for classes, methods, fields and parameters. This feature helps to overcome the language-neutral limitation of the class diagram. The code generation routines can query this information and incorporate the suitable keywords in the generated code.
• Hover-Sense: Provides dynamic help to the user. The user can get the details (such as summary and meta info) associated with a class/methods/fields by hovering the mouse on the respective visual element. The metainfo, which is not depicted in the class diagram, is presented to the user in this form.
• Image Generation in 4 formats: gif, jpeg, png, tiff