The Mobile Gamepad, an Android app, works with server-side application on the host PC, allowing use of different kinds of controls to play games via the smartphone.
Now, you have a mobile app that turns your Android smartphone into a gamepad for a Windows computer. The app, called Mobile Gamepad, has been created by a XDA Forum Member blueqnx and is available via Google Play store.
Once installed, the mobile app turns your device into a motion sensing and customizable gamepad. The app provides a virtual D-pad and siz buttons – square, triangle, circle, cross, pause, and start. You can map the virtual buttons to any key on the keyboard and assign to various profiles.
Mobile Gamepad uses accelerometer in your Android smartphone to enable gamers motion control. To do this, simply enable motion mode, and place your finger where the D-Pad once was. You can use the app to start PC games from the smartphone as well. Other features of the app include support swipe over controls for easy usage not just clicking, device volume buttons to control windows volume.
You can download the Mobile Gamepad app for free via Google Play store. You can find out more details about the application on this thread on XDA Developers.