The iPhone app Rx/Tx is part of my bachelor thesis in Computer Science and Media. It allows users to receive (Rx) and Transmit (Tx) arbitrary files. This is acheived by converting the data into sound on one side and playing it back through the internal speaker. The receiver can then record the sounds and decode them back into the original data. The transmission is enhanced with a simple error correction scheme, allowing for errors to occur and automatically be corrected.
The application was developed to overcome the limitations of file transfer with iOS devices when no internet connection is available. Since these devices do not support Bluetooth file transfer, this method presents an alternative approach for directly transmitting data between two devices. Working prototypes of the encoding and decoding schemes were implemented in Ruby, but were not able to decode in real time; the final product is entirely written in Objective-C.
Unfortunately, the application is not available on the iTunes Store, but here is a video and some screenshots demonstrating how it works.