Microsoft has released a new app called My Server for Windows 8/RT devices which allows you to manage Windows Server 2012.
My Server for Windows 8 is an application designed to help you keep seamlessly connected to your server resources through devices running Windows 8. With My Server, you can manage users, devices, alerts, and access shared files in Windows Server 2012 Essentials. In addition, files that you have recently accessed with My Server files continue to be available to you even when offline.
•Browse, edit and search files stored on your server
•Manage users, devices, and alerts
•Share local resources to server or save server resources locally
•Access files that you opened recently even without an Internet connection. The changes made offline will be automatically synchronized to the server when online
•Playback of media files stored on server
Download it from Windows Store here.