Contents of the "mac" sub-archive for UnZip 5.3 and later:

  Contents          this file
  mac.c             Mac-specific filesystem code
  macdir.c          Macintosh Unix-style directory emulation
  macdir.h          header file for directory emulation
  macscreen.c       Macintosh window handling routines
  macstat.c         Macintosh stat() emulation
  macstat.h         header file for stat() emulation
  macunzip.c        Macintosh standalone version main program
  metrowerks.hqx    Metrowerks CodeWarrior C project file (BinHex)
  rsrc.hqx          resource file for Macintosh unzip (BinHex)
  thinkc.hqx        Think C project file (BinHex)

The resource file and the compiler project files are in BinHex form because
they contain Macintosh resource forks and as such can not be simply
stored a normal file on a non-Macintosh system.  BinHex form is the
traditional way for transferring such files via non-Macintosh systems.
It's also the safest since it uses only printable characters.  The ".hqx"
files must be converted with StuffitExpander or BinHex 4.0 (or equivalent)
on a Macintosh system before using them.