No crux isn't any good IMO. Wayyy too opinionated. Research project at best. 2 years old, 2000 stars, and zero non-trivial projects created using it https://github.com/search?q=crux_core%20path%3Ashared%2FCargo.toml&type=code
I'm prototyping rust-multiplatform here https://github.com/justinmoon/rust-multiplatform