Microsoft is about to release Windows 10 and along with it a version that will run on a raspberry pi 2. A computer not much bigger than a credit card. What was a specialised area of development is now available to developers with c# and xaml knowledge.
This post by the excellent Telerik provides a hello world guide in developing for the device.
At //Build 2015, Microsoft demonstrated a version of Windows running on a Raspberry Pi 2 board.