ASA147 is a MATLAB library which evaluates the incomplete Gamma function.
ASA147 is Applied Statistics Algorithm 147. Source code for many Applied Statistics Algorithms is available through STATLIB.
ASA032 is a MATLAB library which evaluates the incomplete Gamma function.
ASA147 is also available in a C++ version and a FORTRAN77 version and a FORTRAN90 version.
ASA239 is a MATLAB library which evaluates the incomplete Gamma function.
DCDFLIB is a FORTRAN90 library which evaluates and inverts a number of statistical distributions.
GSL is a C++ library which includes many routines for evaluating probability distributions.
PROB is a MATLAB library which evaluates and inverts a number of probabilistic distributions.
TEST_VALUES is a MATLAB library which contains sample values for a number of distributions.
TOMS435 is a FORTRAN90 library which evaluates the modified incomplete Gamma function.
TOMS708 a FORTRAN90 library which includes routines to evaluate the incomplete Gamma function.
You can go up one level to the MATLAB source codes.