To write a GUI (Graphical User Interface) application in Rust, you can use one of several available GUI libraries and frameworks. Here are some popular options:

Cocoa : Cocoa is a macOS native UI framework (not a Rust library) that can be accessed using the cocoa-rs Rust bindings. It allows you to create native macOS applications. However, be aware that using Cocoa directly will be platform-specific and won't be cross-platform.

ImGui : ImGui (also known as Dear ImGui) is a bloat-free graphical user interface library for C++. It is popular for creating graphical interfaces for game development, tools, and applications.

GTK : Gtk-rs is a set of bindings for the GTK library, which is a popular GUI library for creating native-looking and highly customizable interfaces.

Gyscos : gyscos is a TUI (Text User Interface) library for Rust. It builds interfaces in the terminal using different backends (like termion, ncurses)

IUP : IUP (Interface User Portable) is a GUI library initially developed in C to provide a minimalistic and easy-to-use interface. IUP has Rust bindings called iup-rust, which allows you to use IUP for building GUI applications in Rust.