ASA239 is a FORTRAN77 library which evaluates the incomplete Gamma function, by Shea.
ASA239 is Applied Statistics Algorithm 239. Source code for many Applied Statistics Algorithms is available through STATLIB.
ASA239 is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.
ASA032, a FORTRAN77 library which evaluates the incomplete Gamma function.
ASA147, a FORTRAN77 library which evaluates the incomplete Gamma function.
DCDFLIB, a FORTRAN90 library which evaluates and inverts a number of statistical distributions.
GSL, a C++ library which includes many routines for evaluating probability distributions.
PROB, a FORTRAN90 library which evaluates and inverts a number of probabilistic distributions.
TEST_VALUES, a FORTRAN77 library which contains sample values for a number of distributions.
TOMS435, a FORTRAN77 library which evaluates the modified incomplete Gamma function.
TOMS708, a FORTRAN77 library which includes routines to evaluate the incomplete Gamma function.
Original FORTRAN77 version by B Shea; This FORTRAN77 version by John Burkardt.
You can go up one level to the FORTRAN77 source codes.