Prototyping
Framer
https://framer.com/
A prototype tool that bridge the gap between code and design with builtin React code library.
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Figma
Combining UI design, prototyping, and feedback in one web-based tool, Figma is more than a design app. Users can iterate prototypes in collaboration, and provide feedbacks simultaneously. It is catching up with Sketch for the need in large-scale design projects. Figma is free to try with limited projects with paid upgrade per user.
Magic Mirror
Perspective mockups could be created without leaving Sketch app. Magic Mirror adds the functionality of perspective transformation to Sketch artboards. So users can create high-fidelity mockups in perspective. Paid monthly subscription support up to 4x image quality and symbols.
Overflow
User-flow diagramming tool tailored for designers. Works with Sketch, Figma, Adobe XD and Photoshop.