Windows 10X is a new version of Windows 10 designed for dual-screen devices such as Microsoft's upcoming Surface Neo, which will be available from 2020. The "new" operating system will have a custom UI for these devices.
Windows 10X is Windows
At the Surface event, Microsoft he stated that Windows 10X will "support Windows applications", which means that all traditional Windows graphics applications will work just like Windows 10 Home or Professional. It is not a completely new operating system, but a custom version of Windows 10 with a UI designed for foldable devices.
Microsoft told The Verge that Windows 10X will run traditional Windows desktop applications in one container to improve battery life. Windows 10X appears to be based on Windows Core OS.
Optimized for dual screen devices
Windows 10X has a UI "designed and optimized for dual-screen devices, such as the Surface Neo," according to Microsoft.
The Surface Neo is a dual screen device that opens like a laptop. Alternatively, they are like two tablets connected by a joint.
There will be no Live Tiles
Part of optimizing the operating system for dual-screen devices seems to be the removal of Live Tiles. There is a new Start menu with simple icons.
When you start an application, it will start on one side of the device. It's a bit like the Windows 10 Snap feature - apps will open on one screen (or one side of the device) and not on both screens. You can drag the application window in the middle of the screen to display it on both screens. Microsoft says that this will not only enlarge the application window on both screens, but will also "optimize" the application interface so that the application can intelligently exploit both screens.
Windows 10X and dual-screen devices are not currently available. Microsoft will release Windows 10X before the release of the Surface Neo, so developers will have time to try it out and optimize their applications for the new operating system.
Microsoft posted a blog post article for the upcoming Windows 10X, but did not mention many technical details.