Microsoft's next version of Windows, known alternatively as Windows 9 and by the code name "Threshold", is reported to be set for a public unveiling on September 30th.
The report from The Verge's unnamed source adds that the date of the press event might change, but that the plan is to launch a preview version of the next version of Windows for developers on September 30 or shortly after the official reveal. Currently, rumors claim that Microsoft may launch the final version of Threshold, which may or may not get the official name of Windows 9, sometime in the spring of 2015.
Microsoft has already stated that the next version of Windows will bring back a version of the Start menu for the desktop UI that went missing with the launch of Windows 8. It will also have the ability to run Modern apps in windows on the desktop. Rumors about Threshold claim that Microsoft may do away with the Charms bar in Windows 8, along with adding support for virtual desktops and the Cortana digital assistant that's currently being used for Windows Phone 8.1.
Source: The Verge