Classic Shell is a free program that improves your productivity and enhances the usability of Windows.
— Microsoft says than Classic Shell is not compatible with Windows 10. Is it true?
The classic shell won't be available for Windows 10, indeed. However, 3rd party developers have created an application that can be installed on Windows 10 and provide the same functionality... as the classic shell.
The application is actually called Classic Shell and it's available for Windows 10. Use the link below to reach the official website.
Download page: http://www.classicshell.net/