Modelio - Modelio is an open source modeling tool supporting natively UML, BPMN and model exchange with XMI.
Balsamiq - Balsamiq. Rapid, effective and fun wireframing software.
Diagramo - Diagramo is an online flowchart software - diagrams (create, edit and share)
Invision - Prototyping and collaboration for design teams
ARIS Express - ARIS Express is based on the proven ARIS methodology and industry standards.
Zeplin - Collaboration app for UI designers & frontend developers