Here is a list of all files with brief descriptions:

analys.c
analys_s.c	Mesh analysis
anisomovpt.c	Functions to move a point in the mesh (with anisotropic metric)
anisomovpt_s.c	Functions to move a point in the mesh (with anisotropic metric)
anisosiz.c	Fonctions for anisotropic size map computation
anisosiz_s.c	Fonctions for anisotropic size map computation
API_functions.c	C API functions definitions for MMG library
API_functions_s.c	C API functions definitions for MMGS library
API_functionsf.c	Fortran API functions for MMG library
API_functionsf_s.c	Fortran API functions for MMGS library
bezier.c	Functions for Bezier surface computation
bezier_s.c	Functions for Bezier surface computation
boulep.c	Functions for ball of points computation
boulep_s.c	Functions for ball of points computation
chkmsh_s.c	Check the input mesh validity
chrono.c	Simulation of a chronograph
chrono.h
colver_s.c	Functions for vertices collapsing
eigenv.c	Find eigenvalues and eigenvectors of matrix
eigenv.h
gentools_s.c	Generic algebraic and algorithmic tools
hash.c	Functions for hash tables management and tetrahedra packing
hash_s.c	Functions for hash tables management and triangle packing
inlined_functions.h	Inlined Functions
inout.c	Input / Output Functions
inout_s.c	Input / Output Functions
intmet.c	Functions to compute metric interpolation
intmet_s.c	Metric interpolations
isosiz.c	Fonctions for isotropic size map computation
isosiz_s.c	Fonctions for isotropic size map computation
libmmgcommon.h	API header for the common part of the MMG libraries
libmmgs.c	API functions for MMGS library
libmmgs.h	API headers for the mmgs library
libmmgs_tools.c	Tools functions for the mmgs library
libmmgs_toolsf.c	Fortran API functions for MMGS library
libmmgsf.c	Fortran API functions for MMGS library
libmmgtypes.h
librnbg.c	Functions for scotch renumerotation
librnbg.h	Header file for the librnbg.c librnbg_s.c librnbg_3d.c files
librnbg_s.c	Functions for scotch renumerotation
mettools.c	Metric tools for the mmg applications
mmg.c	Common part for functions used in mmgs.c and mmg3d.c files
mmg2.c
mmgcommon.h
mmgexterns.c
mmgexterns.h
mmgs.c	Main file for MMGS executable: perform surface mesh adaptation
mmgs.h
mmgs1.c	Perform surface mesh adaptation
mmgs2.c	Create implicit surface in mesh
mmgsexterns.c
mmgsexterns.h
movpt_s.c	Functions to move a point in the mesh
quality.c	Functions to compute elements quality and edge lengths
quality_s.c	Functions to compute elements quality and edge lengths
scalem.c	Scale and unscale mesh and solution
split_s.c	Functions to create new points
swapar_s.c	Functions for swapping process
tools.c	Various tools for the mmg applications
variadic_s.c	C variadic functions definitions for MMGS library
zaldy_s.c	Memory management