GUI in Rust is a hot topic, and to me it seems SlintUI may be the best general-purpose so far. The reason is rapid iteration and a flexible/intuitive layout system: Slint lets you write UI in a DSL with live preview and style/layout influenced by HTML and CSS, whereas competitors (egui, druid, iced) require you to write the GUI in Rust (which means you must rebuild and rerun to see changes) and have their own style/layout rules. Other competitors are GTK and Qt, but those have their own flaws and moreover, were designed way before Rust and seem to be less "idiomatic".