Part of what sets Windows RT apart from Android, iOS, and other mobile operating systems is that it's basically a full-fledged desktop operating system. Under the hood, it's pretty much the same OS as Windows 8. It's just designed to run on devices with ARM-based chips instead of x86 processors.
Unfortunately, most desktop Windows apps won't run on Windows 8 for two reasons: They're not compiled for ARM processors, and Microsoft only lets Windows RT users install apps from the Windows Store (which doesn't allow desktop apps).
But now that there's a way to jailbreak Windows RT, developers are starting to recompile apps so they can be side-loaded on the Microsoft Surface RT and other Windows RT tablets.