Microsoft has published a new blog post that details the new “Assigned Access” feature in Windows Embedded 8.1 (Pro and Industry). Assigned Access allows you to setup an Windows 8 App as the default shell for a specific user.
Once an assigned access user logs in he is immediately in the configured application (without Start Screen or classic desktop). This enables and easy additional lockdown for specific users!
More details are available in the original post: http://blogs.msdn.com/b/windows-embedded/archive/2013/10/16/windows-embedded-8-1-assigned-access-and-windows-embedded-lockdown.aspx