The public Windows 8 beta will be released in late February of 2012 as per a report by thenextweb. Windows 8 developer edition was make available to public in September. The Windows Developer Preview is a pre-beta version of Windows 8 for developers which was released by Microsoft specifically for developers. Windows 8 is designed to work on both PCs and tablets.
It is previously estimated that Windows 8 should be released to manufacturers (RTM) in June. There has been no confirmed regarding the date of release yet.
Source: The Next Web