[Tools] SmartUML Freehand Sketch-Enabled Multi-User UML Diagram Designer
In Beta 1 is
SmartUML, an interesting new UML diagramming tool. Although no source code is yet provided, the download for this project is on SourceForge, so let's hope it will be Open-Source in the near future.
SmartUML is designed to be Tablet PC friendly, but it can also be used on Windows desktops and laptops.