toms515, a FORTRAN77 code which lists the subsets of size K selected from a set of size N, by Bill Buckles, Matthew Lybanon.
The computer code and data files described and made available on this web page are distributed under the MIT license
toms515 is available in a C version and a C++ version and a Fortran90 version and a MATLAB version and an Octave version and a Python version.
subset, a FORTRAN77 library which enumerates combinations, partitions, subsets, index sets, and other combinatorial objects.
Original FORTRAN77 version by Bill Buckles, Matthew Lybanon. This version by John Burkardt.