As we know that Microsoft has announced Windows 8.1 update for Windows 8 users, on June 26 Windows 8.1 Preview build will be available and RTM will hit later this year. Windows RT is the cut down version of Windows 8 which is specially build for Windows RT tablets.
On Windows RT you can only install apps from Windows Store, Windows RT comes pre-installed with Office 2013 but one thing which is missing on Windows RT is Outlook 2013, so Windows RT users have to use default Mail App for eMailing.
But with Windows 8.1 update Windows RT users will get taste of Outlook 2013, which means if you are using Surfacetablet or any other tablet which runs on Windows RT then you will get Outlook 2013 for free.
Outlook is the one of the best email client in the market as it allows you to do much more than sending email, you can manage your contacts, calendar and appointments within the same window.
Other than Outlook, Office 2013 have Word, Excel, and PowerPoint. There will be some more updates which will be rolled out with Windows 8.1.