GNU unzip is used to, well, unzip the zip files downloaded using the wget tool.

GNU unzip is available for most of the UNIX-like platforms and as the unzip package from the Cygwin setup.

You will only need unzip, if you want to use the Win32 automated library download, see Section 5.3, “Win32: Automated library download” for details.

If GNU unzip isn't already installed or available as a package for your platform (well, for Win32 it is available as a Cygwin package), you can get it at: https://gnuwin32.sourceforge.net/packages/unzip.htm.