Most rumors concerning Windows 9 "Threshold" we heard in the last few months indicated the end of September/early October as the period of its official unveiling. While Microsoft still has to officially confirm this, which will probably happen at the press event itself, Windows 9 should show up at the end of this month.
The press invites sent earlier this week by the Redmond giant read "Join us to hear about what's next for Windows and the enterprise." next to the date of the event and a Microsoft logo. While the highlight of the event is expected to be the preview build of Windows 9, next to the launch date of the final build, there is one more thing.
Various rumors mentioned that Windows RT and Windows Phone will be discontinued and a new OS will launch alongside Windows 9. While Microsoft did not confirm this yet, it is possible to see this show up on September 30 as well. Considering the reference to the enterprise sector, we may even see a new Windows Server version, but all these need to be taken with a grain of salt for the time being. We will get back to this event as soon as more info about it becomes available.