ASA245 is a FORTRAN90 library which evaluates the logarithm of the gamma function, by Allan Mcleod;
ASA245 is Applied Statistics Algorithm 245.
ASA245 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.
FN, a FORTRAN90 library which approximates elementary and special functions using Chebyshev polynomials, by Wayne Fullerton.
GSL, a C++ library which includes many routines for evaluating special functions.
SLATEC, a FORTRAN90 library which evaluates many special functions.
SPECFUN, a FORTRAN77 library which evaluates certain special functions using fitted data.
TEST_VALUES, a FORTRAN90 library which contains sample values for a number of distributions.
TOMS291, a FORTRAN77 library which evaluates the logarithm of the Gamma function.
Original FORTRAN77 version by Allan Mcleod; FORTRAN90 version by John Burkardt.
You can go up one level to the FORTRAN90 source codes.