Windows RT is that version of Windows that runs on low power ARM devices. I think for most people the pros and cons of this architecture are pretty clear already.
Usually the first upside argument is the significantly longer battery life it offers, and that's certainly the case. Windows RT's restricted architecture limits the processes that are running at any given point to only those modern apps that are designed to respect mobile users and their limited batteries. That's a really great thing for users.
Besides the battery argument, however, I have another strong case for Windows RT that I'd like to share. By the way, I work at Microsoft, but I don't have any influence on the teams that make these kinds of decisions, so I'll just say that I hope that the Windows RT level or something like it sticks around. Here's my case.
I have a friend that just installed a new shower for my wife and I. It's a doozy too. Two shower heads and everything. Now we're living in luxury.
This contractor friend of mine and his wife are... how to say nicely... far better with a tile saw than a computer. Computers aren't their thing. At the same time, they run a small business and work with real estate, and so their job demands they spend a certain amount of time in front of a glowing screen.
We all know folks like these who spend 90% of their time in a browser, an email client, and the Office suite. And the other 10% of is spent waiting for the system to boot and launching the browser, email client, or Office suite.
These folks have a hard time getting work done anymore, because they're overwhelmed with malware. Malware sucks, and there's not really a good resolution. No matter what platform or browser is used, the consumer still wields the power to authorize the installation of malware. And if they don't know any better, they will.
But malware is pretty much a moot point in the modern app ecosystem, and Windows RT devices are all but immune to it. The only code that can execute is built in or being executed out of an app package.
We're dealing now with a whole new model for delivering code to people - it's one where code is authorized and restricted. Code has to declare itself and its intent and it has to pass the test.
So, I recommend to my friend that they get a Windows RT device that performs the primary tasks (browser, email, and Office) brilliantly, but doesn't offer any hope at all for the malware authors that would like to ruin their days.
This, in my opinion is a very strong case for this version of the OS.
I can put a Surface RT or some other Windows RT device in the hands of even my closest relatives and not expect support calls with complaints of malware. I'll get support calls for other things I can be sure, but not for malware, and that is a big leap forward in my opinion.