iPhone developer Emanuele Vulcano has been working on a new iPhone OS data exchange protocol called SwapKit [Apple Dev account required for link]. Hosted on GitHub, SwapKit provides App Store-friendly application-independent ways to publish data with custom metadata for sharing between applications.
SwapKit can automatically find all other SwapKit-using applications on a device and determine which of those applications can perform specific actions on that data. For example, a developer might send a string to the first Twitter-ready client it finds and request that client to post the string as a new tweet. SwapKit basically offers a Mac-style LaunchServices for iPhone.
Open source and provided under the MIT license (basically "use however you like"), SwapKit remains in early development. The screencast shown above demonstrates basic SwapKit features, demoing both sending and receiving functionality.