Zeplin - Collaboration app for UI designers & frontend developers
UX Flow Wireframe Prototyping System - Create beautiful user flows prototypes for your next project
avocode - Centralize design collaboration, version control, prototyping, feedback, and developer hand-off with Avocode. Work on any design, anywhere, with anyone. Sign up free 👉 https://avocode.com/.
draw.io - Online diagramming application
Mockplus iDoc - Handoff designs with accurate specs, assets, code snippets
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.