The download link for Web2Executable is https://github.com/jyapayne/Web2Executable.
Web2Executable is a pretty smart NW.js packaging tool written in Python by Joey Paine, a Canadian tech guy. Between the many tools I will introduce you, this is the only one that comes with a quite essential but really usable GUI (if you are not interested in the GUI, you can also download the CLI version).
Web2Executable is available to all the three platforms: Mac OS X, Microsoft Windows 7 +, and Linux (tested on Ubuntu 14.04).
If you decide to run it out of the source code, you will need Python, PySide, and PIL; however, if you download one of the prepackaged executables, it will work out of the box.
What Web2Executable does can be summarized as follows:
Downloading the NW.js package for the given version of the selected platform
Building packages for various platforms
Eventually adding the icon to the Mac OS X and Microsoft Windows executable