Here is a list of all documented files with brief descriptions:

accuracy.c
include/api.h
kernel/nfsft/api.h
assert.c
bessel_i0.c
bspline.c
construct_data_2d.c
construct_data_2d1d.c
construct_data_3d.c
construct_data_inh_2d1d.c
construct_data_inh_3d.c
cycle.h
damp.c
examples/doxygen.c
applications/doxygen.c
applications/mri/doxygen.c
examples/solver/doxygen.h
applications/fastsumS2/doxygen.h
applications/iterS2/doxygen.h
applications/mri/mri2d/doxygen.h
applications/mri/mri3d/doxygen.h
applications/polarFFT/doxygen.h
applications/quadratureS2/doxygen.h
error.c
fastsum.c	Fast NFFT-based summation algorithm
fastsum.h	Header file for the fast NFFT-based summation algorithm
fastsum_benchomp.c
fastsum_benchomp_createdataset.c
fastsum_benchomp_detail.c
fastsum_matlab.c	Simple test program for the fast NFFT-based summation algorithm, called by fastsum.m
fastsum_test.c	Simple test program for the fast NFFT-based summation algorithm
fastsumS2.c
flags.c	Testing the nfft
float.c
fpt.c	Implementation file for the FPT module
fpt.h
infft.h
int.c
iterS2.c
kernels.c	File with predefined kernels for the fast summation algorithm
kernels.h	Header file with predefined kernels for the fast summation algorithm
lambda.c
legendre.c
legendre.h
malloc.c
mri.c
ndft_fast.c	Testing ndft, Horner-like ndft, and fully precomputed ndft
nfct.c
nfft.c
nfft3.h
nfft3mp.h
nfft_benchomp.c
nfft_benchomp_createdataset.c
nfft_benchomp_detail.c
nfft_times.c
nfsft.c	Implementation file for the NFSFT module
nfsft_benchomp.c
nfsft_benchomp_createdataset.c
nfsft_benchomp_detail.c
nfsoft.c
nfst.c
nnfft.c
nsfft.c
nsfft_test.c
print.c
quadratureS2.c
rand.c
reconstruct_data_2d.c
reconstruct_data_2d1d.c
reconstruct_data_3d.c
mri2d/reconstruct_data_gridding.c
mri3d/reconstruct_data_gridding.c
reconstruct_data_inh_2d1d.c
reconstruct_data_inh_3d.c
reconstruct_data_inh_nnfft.c
fpt/simple_test.c
nfsft/simple_test.c
nfsoft/simple_test.c
nnfft/simple_test.c
nsfft/simple_test.c
simple_test_threads.c
sinc.c
solver.c	Implementation file for the solver module
solver_adjoint.h	Header file for adjoint solver
sort.c
taylor_nfft.c	Testing the nfft againt a Taylor expansion based version
thread.c
time.c
vector1.c
vector2.c
vector3.c
version.c
voronoi.c
wigner.c
wigner.h	Header file for functions related to Wigner-d/D functions
window.c