NWChem launched from Winmostar are supposed to be compiled and installed.
NWChem is disistributed under Educational Community License 2.0, and is available for free.

The program is confirmed to run on Windows 10 (64 bit).
Please understand that calculation results are not guaranteed.

　1. Installation

We are going to build NWChem 6.6 basically following the instruction on the official site below.
http://www.nwchem-sw.org/index.php/Compiling_NWChem#How-to:_Windows_Platforms

　1-1. MinGW

Download mingw-get-setup.exe from https://sourceforge.net/projects/mingw/files/Installer/ .
Follow the wizard and install it.
The packages which need to be installed are follows.
・all packages in [Basic Setup]
・mingw32-pthreads-w32, mingw32-gcc-fortran-dev in [All Packages]-[MinGW]

　1-2. MPICH2

MPICH2 is available for MPI parallelization.
Download https://www.mpich.org/static/downloads/1.4.1p1/mpich2-1.4.1p1-win-ia32.msi and install it.

Launch C:\MinGW\msys\1.0\msys.bat to use it as a terminal.

$ cp -rp /c/Program\ Files\ $x86$/MPICH2/ ~/

　1-3. Python

Download https://www.python.org/ftp/python/2.7.8/python-2.7.8.msi and install it.

　1-4. Compile NWchem

Download NWChem 6.6 source code (tar.gz file) from http://www.nwchem-sw.org/index.php/Download#NWChem_6.6_Source_Code .

Download all patch files.
Put them in your home directory.

Patch it as follows.
$ for f in *.gz; do gunzip $f; done
$ tar Nwchem-6.6.revision27746-src.2015-10-20.tar.gz
$ mv *.patch nwchem-6.6/
$ cd nwchem-6.6
$ for f in *.patch; do patch -p0 < $f; done

$ vim nwchem_env.sh
export NWCHEM_TOP=~/nwchem-6.6
export NWCHEM_TARGET=LINUX
export USE_MPI=y
export MPI_LOC=~/MPICH2
export MPI_INCLUDE=$MPI_LOC/include
export MPI_LIB=$MPI_LOC/lib
export LIBMPI="-lfmpich2g -lmpi"
export PYTHONHOME=/c/Python27/
xport PYTHONVERSION=27
export DEPEND_CC=gcc
export NWCHEM_MODULES=all
export USE_INTERNALBLAS=y

$ . nwchem_env.sh

Compile it as follows.
$ cd src
$ make nwchem_config
$ make FC=gfortran DEPEND_CC=gcc

Install it as follows.
$ mkdir -p /c/nwchem/bin
$ mkdir -p /c/nwchem/data
$ cp $NWCHEM_TOP/bin/${NWCHEM_TARGET}/nwchem /c/nwchem/bin
$ chmod 755 /c/nwchem/bin/nwchem
$ cp -r $NWCHEM_TOP/src/basis/libraries /c/nwchem/data
$ cp -r $NWCHEM_TOP/src/data /c/nwchem
$ cp -r $NWCHEM_TOP/src/nwpw/libraryps /c/nwchem/data
$ vim /c/nwchem/data/default.nwchemrc
nwchem_basis_library /c/nwchem/data/libraries/
nwchem_nwpw_library /c/nwchem/data/libraryps/
ffield amber
amber_1 /c/nwchem/data/amber_s/
amber_2 /c/nwchem/data/amber_q/
amber_3 /c/nwchem/data/amber_x/
amber_4 /c/nwchem/data/amber_u/
spce /c/nwchem/data/solvents/spce.rst
charmm_s /c/nwchem/data/charmm_s/
charmm_x /c/nwchem/data/charmm_x/