Windows 8
Windows 8 is the basic edition of Windows. This edition contains features aimed at the home users and provides all of the basic new Windows 8 features including the Start screen with semantic zoom, live tiles, Windows Store, Internet Explorer 10, connected standby, Microsoft account integration, the Windows desktop and more.

Windows 8 Pro
Windows 8 Pro is comparable to Windows 7 Professional and Ultimate and is targeted towards enthusiasts and business users; it includes all the features of Windows 8. Additional features include the ability to receive Remote Desktop connections, the ability to participate in a Domain, Encrypting File, Hyper-V, Group Policy, as well as  BitLocker.

Windows 8 Enterprise
Windows 8 Enterprise provides all the features in Windows 8 Pro (except the ability to install the Windows Media Center add-on), with additional features to assist with IT organization. This edition is available to Software Assurance customers, as well as MSDN and Technet Professional subscribers.

Windows RT
Windows RT will only be available pre-installed on ARM-based devices such as tablet PCs. It will include touch-optimized desktop versions of the basic set of Office 2013 applications to users and support device encryption capabilities. Several business-focused features such as Group Policy and domain support are not included.
Desktop software that run on previous versions of Windows cannot be run on Windows RT.

Unlike Windows Vista and Windows 7, there are no Starter, Home Basic, Home Premium, or Ultimate editions.