Microsoft is set to release Windows 8 on October 26th, meanwhile the operating system has been released to manufacturing (RTM). However if you are a developer with an MSDN Subscription or TechNet Professional Subscription, you can download Windows 8 RTM right now.
Windows 8 is one of the biggest visual updates to the Windows user interface. The new live tiled UI is inspired by Windows Phone and will be available through a varied selection of form factors including the Windows RT based ARM tablets.
By releasing the RTM Microsoft allows developers to test their applications with the latest version of Windows and ensure that these apps will be ready for the public on October 26th.
source – Microsoft