This .zip archive contains DLL libraries and the associated header (.h)
and module-definition (.def) files of NLopt compiled for Win64.

In order to link to this .dll files from Visual C++, you need to
create a .lib "import libraries" for it, and can do so with the "lib"
command that comes with VC++.  In particular, run:
     lib /def:libnlopt-0.def

To compile the Matlab plugin, use the Matlab "mex" compiler on the file
nlopt_optimize.c (being sure to link to the libnlopt DLL) in the matlab
subdirectory.

To build the Python plugin (assuming that you have Python and Numpy
installed), do:
   python setup.py build_ext --inplace

They were compiled by the GNU C compiler for MinGW, specifically:
x86_64-w64-mingw32-gcc (GCC) 4.6.3