If you have Windows Phone 8.1 and have been dying to try out the Project my Screen feature today is your lucky day.
The download is currently available on Microsoft’s servers here, and it seems to work pretty well.
Unfortunately the app is a Windows desktop app, not Windows Metro, but is still full screen on the desktop, making meaning you can not snap the app to the side of your screen or open it in a window and still get other work done.
To use the feature, install the Project My Screen app, activate Project My Screen in Settings on your phone, and connect your phone and run the app on your desktop.
Update: Alt+Enter will return the app to windowed mode on the desktop, which has just made the app 1000% more useful.