I have been using Microsoft’s Garage Mouse Without Borders to remotely control PCs from one keyboard and mouse for a while. It works very well for controlling a HTPC from another PC and I love how you can move the mouse off one screen to another.
I just found out that as well as the Windows versions (with run under Windows 7 and Windows 8) there is a Windows Phone app. With the app you control the host PC from the phone, it turns your Windows Phone into a trackpad for the PC and there is also an on screen keyboard.
To get it working you install the app on your Windows Phone and install Mouse Without Borders on your PC (if you haven’t already). Once you have the PC running you right click on the icon in the tray and select Enable from the Win Phone/Win8 Tablet and then from the same menu select Information. Then go to your Windows Phone and enter the IP address of your PC into the app and enter the 3 digit code from the Information window on the host PC. Then you can control your PC from the Phone.
As well as the Windows Phone app there is also a Windows Store app that will run on Windows 8 and Windows RT. This has the same features as the Windows Phone version and connects the same way. The best news of all is that the PC app is free as are the Windows Phone and RT apps so give it a try.
The Windows Phone app works on Windows Phone 7.5 and Windows Phone 8.