Monect - Make the best use of sensors on smart device to control PC, simulate steering wheel, game-pad...
LEA Extended Input - iOS/Android app with windows server to control functions in games via your smartphone/tablet.
Wifipad - WifiPad transforms your iPhone/iPod Touch into a wireless gamepad.
Pcon - Control your PC with your Android device.
Unified Remote - Unified Remote is a software app available for iPhone, Android, and Windows Phone mobile operating systems. It's designed to turn your smartphone into a universal remote. Read more about Unified Remote.
nJoy - Complete PC remote controlling solution for Android.