Classic Shell website says:
What are the system requirements of Classic Shell?
Classic Shell supports Windows 7, Windows 8, Windows 8.1, Windows Server 2008 R2, Windows Server 2012 and Windows Server 2012 R2. There is only one installer for all and it covers both 32-bit and 64-bit operating systems. Not all features are supported for all versions of Windows.
Does Classic Shell support Windows 10?
Starting with version 4.2.1, Classic Shell supports Windows 10 TP build 10041 and later. Of course, since Windows 10 is not officially released, glitches are possible.
Does Classic Shell support Windows RT?
No, Classic Shell does not work on Windows RT (either 8 or 8.1). There are two reasons for that. First, Windows RT runs on devices with a different CPU, which is incompatible with regular Windows applications. And second, Windows RT does not allow non-Microsoft software to run on its desktop.
Is Classic Shell Free?
Yes, Classic Shell is free for both personal and commercial use*.
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John