Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Invision - Prototyping and collaboration for design teams
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
ARIS Express - ARIS Express is based on the proven ARIS methodology and industry standards.
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project