https://system76.com/cosmic

https://helix-editor.com/

https://zed.dev/

Well, what about small CLI tools, like ripgrep and the like? Does multithreading not matter when we open a large number of files and process them? What about compilers?

You might start with https://github.com/zed-industries/awesome-gpui and https://blog.logrocket.com/state-rust-gui-libraries/