Astade: a platform-independent UML-tool for C++, based on wxWidgets.
ATL - a tool which can transform UML models into other models. Available from the Eclipse M2M project (Model to Model).
BOUML: multi-platform UML 2.0 toolbox. Can generate C++/Java/IDL/PHP/Python and reverse engineer C++/Java/PHPhttp://bouml.free.fr/doc/index_phpreverse.html. Very high performance (written in C++ with Qt). Licensed under the GNU GPL.
Dia: a GTK+/GNOME diagramming tool that also supports UML (licensed under the GNU GPL)
Eclipse: with Eclipse Modeling Framework (EMF) and UML 2.0 (meta model without GUI) projects.
Eclipse Uml2Tools: GUI for the Eclipse UML2 Implementation with 5 diagram types
PyUML: Graphical UML Editor plugin for Eclipse based on Eclipse UML2Tools that supports Python roundtrip, views and live validation
Fujaba: Acronym for "From UML to Java And Back Again". Allows modeling behaviour using story diagrams.
NetBeans: available in NetBeans 6.0 full edition, or as a downloadable plugin in Plugin Manager, or with NetBeans IDE 5.5 Enterprise Pack
Papyrus: an open source UML2 tool based on Eclipse and licensed under the EPL (www.papyrusuml.org). See also Topcased below.
StarUML: an open-source UML/MDA platform for Microsoft Windows, licensed under a modified version of GNU GPL, mostly written in Delphi
Taylor: model-driven architecture "on rails" (licensed under the GNU LGPL)
Topcased: www.topcased.org Set of eclipse-based open source model editors, transformation and formal verification tools. Modelling languages include SysML. Development sponsored by European aerospace manufacturers. A merge with Papyrus is in preparation (2007).
UmlGraph: an open source tool suite, which allows the declarative specification and drawing of UML class and sequence diagrams.
UMLet: a Java-based UML tool (licensed under the GNU GPL)
Use Case Maker: a use cases management tool (licensed under the GNU LGPL)
Violet UML Editor: an easy-to-use Java-based UML Editor; fully integrated into Eclipse; licensed under the GNU GPL
Xholon: an open source tool that transforms, simulates and executes models developed using third-party UML 2.0 modelers
Proprietary UML tools
Potential users can freely download versions of most of the following tools; such versions usually impose limits in capability and/or by a time-period.
BLU AGE: an MDA compliant software workbench that enables 100% automated transformation of your UML 2.X diagrams into Java EE and .Net Enterprise business applications.
Blueprint Software Modeler: An integrated software-modeling environment with UML 2.1 modeling, OCL 2.0, meta-modeling and profiles; based on Eclipse
Borland Together: UML modelling tool, integrated with Eclipse and with MS VS.NET 2005. Supports UML 2.0 and MDA, OCL, MOF.
MasterCraft (software): a suite of tools from Tata Consultancy Services Limited which support object-oriented analysis and design using UML for development of MDA-based application-software. The tool-suite consists of IDE-based modelers which allow for UML-based modeling.
Metamill: a round-trip UML tool for C++, C# and Java. Runs under Windows and Linux.
MicroGOLD WithClass: UML modeling tool that can generate code and reverse engineer C++, Java, Delphi, VB, IDL, Perl, PHP, C#, and VB.net. Works with EJB.
TextUML Toolkit: a tool for creating UML 2.1 models using a textual notation.
TopCoder UML Tool tool designed and developed entirely by the TopCoder Community to model sequence, class, use case, and activity diagrams. Free and open-source but with a specific license agreement
Trace Modeler: an easy-to-use and smart editor for UML sequence diagrams. It's lightweight, portable and ensures diagrams are always visually pleasing and structurally correct. 30 sec demo.
Use Case Studio: a use-case authoring tool by Rewritten Software. Free for educational use.