Atomic - The fastest way to design beautiful interactions
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
Dotgrid - A simple vector illustration tool.
Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Invision - Prototyping and collaboration for design teams
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.