Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
Sketch - Professional digital design for Mac.
UML Designer - UML Designer provides a set of common diagrams to work with UML 2.5 models.
Invision - Prototyping and collaboration for design teams