Windows RT can't be purchased directly; it's only found preinstalled on ARM processor-powered Windows RT tablets such as the Microsoft Surface RT. Windows RT largely mimics Windows 8, but unlike its PC-focused counterparts, Windows RT cannot run traditional desktop programs. Instead, it can run only the Modern-UI-style Windows 8 apps found in the Windows Store, and while the Windows Store's app selection is improving, it's still generally lacking in both quantity and quality.
The inclusion of the Office Home and Student RT suite is a major boon for Windows RT tablets, but licensing technicalities stamp out its legal use in the workplace.
"As sold, Office Home & Student 2013 RT Preview and the final edition are not designed for commercial, nonprofit, or revenue-generating activities," explains the Office Home & Student RT FAQ page. "However, organizations who purchase commercial use rights or have a commercial license to Office 2013 suites can use Office Home & Student 2013 RT for commercial, nonprofit, or revenue-generating activities."
Major bummer. Be sure to keep those considerations in mind when you're choosing between Windows RT and Windows 8 tablets for your company. With full-fledged Windows 8 tablets like the Acer W510 and Dell Latitude 10 starting to show up for $500--roughly the same price as a Windows RT tablet--it's hard to recommend picking up a Windows RT tablet for your business.
Follow the proper path, young grasshopper
While you're deciding which version of Windows 8 is right for your SMB, keep in mind that your current Windows 7 installation may constrain your Windows 8 upgrade path. The chart above comes from the surprisingly comprehensive Wikipedia entry on the various Windows 8 editions, which also includes a massive spreadsheet that visually details which features are available in which editions of the operating system. While it's a bit light on information about the specific utilities, it's a very handy resource for comparing the feature sets of Windows RT and the various Windows 8 editions at a glance.