toms451, a FORTRAN77 code which implements ACM toms algorithm 451, which evaluates quantiles of the Chi-Square probability distribution.
The text of many ACM toms algorithms is available online through ACM: http://www.acm.org/pubs/calgo or NETLIB: http://www.netlib.org/toms/index.html.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
toms451 is available in a FORTRAN77 version.
prob, a FORTRAN90 library which contains numerous routines for handling the Chi square distribution and other probability distributions.
TEST_VALUES, a FORTRAN90 library which contains routines which return sample values of various functions, including the modified beta function, and the logarithm of the gamma function.