Smartphones as Game Controllers 14 years ago
There's several apps out there that do this, with what appears to be only limited interest.
I created one myself as a side project - to suit only my favourite type of game, driving games (www.mungoscott.com). Using an iPhone as a steering wheel avoids some of the issues with no tactile feedback, because the entire device is the control. It works very well for driving simulators and games, but I haven't worked out how it could be useful for say a first person shooter - the latency alone (typically 5 to 10ms) is less than ideal for a good FPS.