Are there any software development tools that can be used to diagram the MVC paradigm?

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Any professional diagramming tool will have development-related diagrams. Try OmniGraffle.

You can drop a project onto graffle and it will build class diagrams for you. Very sexy.

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Assuming your real question was about CASE tools – No. I know of no tools for the mac that can generate code from a diagram.

ArgoUML [http://argouml.tigris.org/] generates Java from the diagrams.

Dia [http://www.gnome.org/projects/dia/] with Dia2Code [http://dia2code.sourceforge.net/index.html] can do that for Ada, C, C++, Java, PHP, Python, shapefile, SQL and C#