Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
AnyLogic - AnyLogic has changed simulation modeling and expanded its application into complex business environments. The unmatched flexibility of multimethod modeling allows users to capture the complexity of virtually any system, at any level of detail.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
ns-3 - a discrete-event network simulator for internet systems
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.
NetSim - NetSim software was created to simulate various Cisco systems. Cisco software is known around the world as being one of the best network, routing and switch systems for businesses and private use. Read more about NetSim.