At an event in May that was focused on the educational market, Microsoft announced Windows 10 S, a version of the operating system that can only run apps from the Windows Store. While the Surface Laptop was the first device to launch with the OS, and some new education-specific PCs were announced today, the firm didn't actually release any images of Windows 10 S until last week when ISOs were made available to MSDN subscribers.
However, an MSDN license is pretty expensive, and you need a yearly subscription plan to access those images. Today though, Microsoft finally opened up Windows 10 S installations to everyone.
Unfortunately, the only users that aren't eligible are Windows 10 Home customers. You'll need to be running Windows 10 Pro, Pro Education, Education, or Enterprise.
After the ISO was offered to MSDN subscribers last week, it was leaked pretty quickly, but if you installed it, you'd see that it's not activated. The good news is that if you use this method, Windows 10 S will indeed be activated after installation.
And once Windows 10 S is activated on your machine, you should be good to go with any future installation of the OS. You can also switch right back to Windows 10 Pro via the Windows Store, since your PC should already be licensed for that.
According to the documentation, this method is meant to be used for PCs in education to test compatibility, although it will work for anyone. Microsoft warns that some peripherals that require custom drivers may not work properly, and some drivers may not work at all.
With your new Windows 10 S installation, you can do pretty much anything that you can do with Windows 10 Pro besides running Win32 apps and joining a domain. You can use Hyper-V to set up VMs, and you can even enroll your PC in the Windows Insider Program.