ASA239 is a FORTRAN90 library which evaluates the incomplete Gamma function, by Shea.
ASA239 is Applied Statistics Algorithm 239.
ASA239 is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version.
ASA032, a FORTRAN90 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 FORTRAN90 library which contains sample values for a number of distributions.
TOMS435, a FORTRAN77 library which evaluates the modified incomplete Gamma function.
TOMS708, a FORTRAN90 library which includes routines to evaluate the incomplete Gamma function.
Original FORTRAN77 version by B Shea; FORTRAN90 version by John Burkardt.
You can go up one level to the FORTRAN90 source codes.