Open source modeling tools
Umbrello, a GPL modelling tool. Runs under (requires) KDE and Linux. Also supports code generation as well as reverse engineering (code to UML) for C++ and Java. http://uml.sourceforge.net
Violet, a very simple GPL drawing tool. Very simple to use/learn. The Violet UI is different; try both and see which you like more. (Roses are Rational, violets are GNU, ... get it?) http://horstmann.com/violet
UMLet, a small, very simple, and easy-to-use drawing tool.There's no real learning curve. http://www.umlet.com
ArgoUML, a free research modelling tool; fairly fully featured. http://www.argouml.org
DIA, a GPL drawing tool based on GTK; supports UML and other diagrams; this is intended to be a freeware Visio-like drawing tool rather than a modelling tool http://www.lysator.liu.se/~alla/dia/
