Unlike version 372, the mzscheme language does not include set-car! or set-cdr!, and cons makes immutable pairs, as in scheme/base; those changes make modules built on mzscheme reasonably compatible with modules built on scheme/base.
Otherwise, the mzscheme language shares many bindings with scheme/base. It renames a few bindings, such as syntax-object->datum instead of syntax->datum, and it provides old versions of some syntactic forms, such as lambda without support for keyword and optional arguments. In addition, mzscheme includes all of the exports of racket/tcp and racket/udp.