Early versions of Windows

Until the release of Windows 1.0, there was a line of operating systems called Microsoft Interface. After planning for Windows 1.0 to release in 1985 the MS Interface OSes were renamed to the Windows 0 line with the release of Windows 1.1. Trough there isn't any OS called Windows 0.0.

OSes

 * Windows 0.1 (formerly known as Microsoft Interface 1.0)
 * Windows 0.5 (formerly known as Microsoft Interface 1.5)