Ah this is for embedded apps. Pretty neat!

It also supports iOS, macOS, Android, Windows, Linux, XBox for Three.js games, as well as (some) Node.js apps.

could you throw a react project (WEB) at it and get a native macos project out of it?

It supports Gea frontends (https://geajs.com). Technically it could compile React with a plugin, but that is left to the community as an exercise :)