Marvel - Turn sketches, mockups and designs into web, iPhone, iOS, Android and Apple Watch app prototypes.
UX Flow Wireframe Prototyping System - Create beautiful user flows prototypes for your next project
Icons8 Lunacy - Free graphic design software with built-in resources. Fully compatible with Sketch and works offline
draw.io - Online diagramming application
Flinto - The prototyping tool designers have been waiting for.
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.