It would appear that the rumors of Windows RT's demise have been greatly exaggerated. The dead OS is showing signs of life as Windows 10 RT. Windows RT, announced and released in 2012, was designed to bring Windows to ARM based processors. User adoption was extremely low, as the OS looked exactly like Windows 8; however, it was only able to run apps that were available in the Store, as well as Office RT, which came preinstalled.
The most notable Windows RT devices were Surface RT, Surface 2, and Nokia Lumia 2520; however, there were a number of third party devices as well. Due to that extremely low adoption, all third party OEMs (except Nokia, who was later bought by Microsoft) backed away from the platform within months.