mzc is a compiler that takes MzScheme source code and produces either platform-independent byte code compiled files (.zo files) or platform-specific native code libraries (.so or .dll files) to be loaded into MzScheme.
mzc works on either individual files or on collections. (A collection is a group of files that conform to MzScheme's library collection system; see library collections in PLT MzScheme: Language Manual).
As a convenience for programmers writing low-level MzScheme extensions, mzc can compile and link plain C files that use MzScheme's escheme.h. This feature is described in Inside PLT MzScheme.