PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
draw.io - Online diagramming application
ARIS Express - ARIS Express is based on the proven ARIS methodology and industry standards.