Microsoft is working on a new all-cloud operating system, something unearthed by Brad Sams on Thurrott, with the new OS referred to as Windows Cloud.
Windows Cloud looks identical to Windows 10, except that it works completely differently - as it is capable of running UWP apps only. This means that non-UWP apps do not work at all, and an error message will display that says 'The app you're trying to run isn't designed for this version of Windows'.
Inside, the new all-cloud OS is going to be an interesting future for Microsoft - as it will be exclusive to UWP applications. Sams got Windows Cloud from a "third-party and not directly from Microsoft" - adding that it "is possible that this is a hacked together build but we won't know until we get our hands-on an official release".