Microsoft Windows 10. (All versions)
Microsoft Windows 10 is no longer just an OS it is now a service, just like the new Office 365. Microsoft charges their customers monthly or yearly to use office 365 also known as the "service". I have a hunch that it won't be long before Microsoft will charge customers to use Windows as well. I switched to Linux almost immediately after the release of Windows 10 and would never go back. Something tells me if that happens Linux will become very, very, popular.