Zed (https://zed.dev) is a GUI built in rust. Im not an expert in GUI building so maybe I'm wrong and they used a separate language for the GUI.

They use Rust, but they basically reinvented the wheel for everything they did, because the existing GUI stuff in the rust ecosystem sucked so badly it wasn't worth fixing.

Which is great, Zed's stack is pretty damn good. But like anything not yet widely used outside of its original use case, it can be rough around the edges, and just plain doesn't support anything that is not needed by Zed.

They use rust for the gpu

https://github.com/zed-industries/zed/tree/main/crates/gpui

See the discussion on a collection of elements ontop

https://news.ycombinator.com/item?id=45719004