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UX Flow Wireframe Prototyping System - Create beautiful user flows prototypes for your next project
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Balsamiq Mockups 3 - New public beta for the popular prototyping tool
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
React Proto - React application design and prototyping tool