ArgoUML is a great UML (Unified Modeling Language) tool. Written in Java and using Java Web Start makes it easy to work with (install) and use on any platform. It has full support for the UML 1.4 standard and provides excellent features to drawing and manipulating you UML diagrams. Like many other UML tools of this caliber ArgoUML provides code generation.

The following programming languages are support for code generation: Java, C++, C# and PHP. The Java support is best since it can be used for round-trip engineering using the reverse engineering feature. ArgoUML also has partial support for user models such as decision model, goals model, etc. Finally diagrams can be exported in many graphical formats, primarily GIF, PNG, PS and SVG.