| Object Management Group (OMF) | The industry consortium responsible for the publishing of the Unified Modeling Language (UML), the Meta-Object Facility (MOF) and the eXtensible Metamodel Interchange (XMI) specifications. I've also heard they do stuff with CORBA. |
| Umbrello | The open source UML modeling application for KDE. This application is probably the primary raison d'etre of the OMF. |
| Rational Software | Now owned by IBM, one of the largest purveyors of UML related software and material in the marketplace. |
| ArgoUML | A Java-based UML modeler. Quite mature. Quite popuar. Get's a lot of attention in the academic research community. |