Sauron native is described as 'cross platform, truly native GUI library for Rust. It extends the Sauron web framework which is heavily inspired by The Elm Architecture' and is an app in the Development category. There are four alternatives to Sauron native for Linux, Mac and Windows. The best alternative is OrbTk, which is both free and Open Source. Other great apps like Sauron native are WebRender (Free, Open Source), Conrod (Free, Open Source) and Azul.rs (Free, Open Source).
The Orbital Widget Toolkit is a multi platform (G)UI toolkit for building scalable user interfaces with the programming language Rust. It's based on the Entity Component System Pattern and provides a functional-reactive like API.