Open-source code generator for Simulink/Stateflow
A free cross-platform editor for the DRAKON visual language.
A PlantUML editor written in Qt4
A modeling tool for software engineers (OO)
Code generation from UML to any language (Java, Objective-C, PHP...)
Repository for dependencies between software design artefacts
PetriNetExec a library for embedding Petri Nets into Java applications
Uses GraphViz to draw UML class diagrams