User interface (UI) design tools are software applications that help designers create and prototype user interfaces. These tools typically include features for creating wireframes, mockups, and prototypes, as well as for testing and iterating on designs.

There are many different UI design tools available, each with its own strengths and weaknesses. Some of the most popular UI design tools include:

Figma: A cloud-based tool that is popular for its collaboration features and its ability to create high-fidelity prototypes.
Sketch: A Mac-only tool that is known for its powerful vector drawing tools and its large library of plugins.
Adobe XD: A vector-based tool that is part of the Adobe Creative Cloud suite. It offers a wide range of features for UI design, including the ability to create interactive prototypes.
Axure RP: A powerful tool for creating high-fidelity prototypes that can be exported to HTML and JavaScript.
Framer: A tool that combines vector drawing with code to create interactive prototypes.