Developer Rogue Amoeba announced some unfortunate news today: Apple has removed its Airfoil Speakers Touch app from iTunes. The software, first released in 2009, allowed users to share audio between various devices by taking advantage of Apple's AirPlay streaming protocol. When paired with the Airfoil desktop client, the free app could receive and play audio from a PC, Mac, or even another iOS device. That's a good deal more functionality than what Apple presently offers through AirPlay — iOS devices are permitted only to beam content to the Apple TV, dedicated speakers, and other outside hardware, with no option to act as a receiver.

Despite being warned of the pending takedown two days ago, the developer still hasn't gotten a satisfactory explanation as to why Apple felt compelled to pull the app. "As far as we can tell, Airfoil Speakers Touch is in full compliance with Apple’s posted rules and developer agreements," writes Paul Kafasis. Airfoil Speakers Touch was last updated (and approved) last month. Rogue Amoeba has filed an appeal with Apple's App Review Board, though cautions that it ultimately has little recourse should Apple uphold its decision. This actually marks the second time the app has been booted from the App Store; it was briefly pulled after being launched in 2009. In that situation, Apple eventually reversed course and reinstated the app after changing an undisclosed company policy.

Assuming what Kafasis says is true and Airfoil Speakers Touch wasn't in violation of Apple's Review Guidelines, the removal could feasibly be a preemptive step as we head into WWDC and a rumored preview of iOS 6. If Apple is planning to expand on AirPlay's features with the next version of its mobile OS, it wouldn't be outrageous to think that the company would prefer to avoid duplicate functionality within third-party apps. Still, that's little more than speculation at this point, and there's also the possibility that Apple is just now discovering something inside the app it doesn't like. More on this situation as it develops.