CanvasUML is a free Cocoa-based application for Mac OS X Tiger that allows you Create simple UML Class Diagrams.
CanvasUML is alpha-quality software and should not be used for mission critical work (as if there were such a thing as mission critical UML diagramming?). CanvasUML is built using Apple's WebKit framework, tag, WebKit's support for ContentEditable.
CanvasUML should be thought of as an exploration of what is possible using the above technologies rather than a solid app. It is basically an experiment to see how far the element can be pushed.
