Windows RT (and Windows RT 8.1) is available on several devices that run ARM processors. Standard Windows will not run on an ARM processor so this special version of Windows 8 was created to do just that and dubbed "Windows RT".
You cannot run x86 apps on Windows RT. Just apps that are available to download through the Windows Store.
The original Surface and the Surface 2 run Windows RT (and Windows RT 8.1)
Also, the Asus Vivotab RT, Dell XPS 10, Ideapad Yoga 11, Samsung Ativ Tab and Nokia 2520 were the devices made to run Windows RT.