IrcamLab has released The Snail version 2, which they describe as an advanced audio analysis and instrument tuning application for iPhone. Here's the details in their own words...
As an analogue of the human cochlea where the different frequencies are split-up and analyzed, The Snail for iPhone uses a snail grid to visualize root note and overtone structures of an incoming sound very precisely via the integrated iPhone microphone. The Snail is based on newly developed audio technology making instrument tuning easy and audio analysis musical and fun to watch.
Tune any instrument with pristine precision
Version 2 offers an additional guitar tuning mode that is available in the tuning view. Just tap on a dedicated string name, play a note and adjust the guitar tuning accordingly. Another major improvement is the new split window mode. Whenever you do any adjustments to parameters you now see how the edits affect the visualization in the upper section. This works in both visualization modes. One mode is the snail grid, a complete musical overview of the audio spectrum. The other one, the tuner view, is especially designed to focus on the root note for tuning purposes. In both views there is a sine tuning oscillator available which is controlled simply by touching the desired note on the iPhone display. There are a lot of customizable parameters. No problem if you would like to tune transposing instruments or if you need a tuning reference other than 440 Hz.
The well-known Ircam institute for acoustic and music research in Paris is responsible for the new technology of detection and visualization. It is a patented invention by Thomas Hélie, CNRS researcher at the Sciences and Technologies for Music and Sound (STMS) Laboratory (IRCAM/CNRS/UPMC/French Ministry of Culture and Communication). Berlin-based company SKYLIFE is responsible for the iOS port of this Ircam technology. The Snail is also available for Mac and PC distributed by Plugivery.
Pricing and Availability:
2.99$ / 2.39€ as a download from Apple's App Store.