Conrod is described as 'portable, 2D, GUI library for the Rust programming language. It provides an immediate-mode API that wraps a retained-mode widget state graph' and is an app in the Development category. There are four alternatives to Conrod for Linux, Mac and Windows. The best alternative is Azul.rs, which is both free and Open Source. Other great apps like Conrod are OrbTk (Free, Open Source), WebRender (Free, Open Source) and Sauron native (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.