Worth noting that bjz is a compiler hacker, and this is a list of "languages" from a language implementor's perspective. From the perspective of a user of the language, nearly all of these are just "Rust, the language"; to a user there's no such thing as e.g. a "trait language" or an "attribute language", there's just Rust, which has traits and attributes in the same way that JavaScript has objects and closures without having an "object language" or "closure language". Of the things that can be described as actual languages there, Unsafe Rust is just a minimal superset of Safe Rust, whereas Const Rust is just a subset of Safe Rust; it's not three languages to learn, it's one language where a handful of things are either available or not in certain contexts. The one thing that legitimately is its own language is the macro-rules language, which is a DSL for syntax manipulation.