Windows 2

from The Free On-line Dictionary of Computing (8 July 2008)

Windows 2
Windows/286

   <operating system> The second version of {Microsoft Windows},
   released in 1987.  Windows 2 had considerably more features
   than {Windows 1}, such as overlapping windows and {icons}.
   When {Windows/386} was released, Windows 2 was renamed
   Windows/286.