Lambda

Musicians and Sound Engineers. Musical Notes and Frequencies and Wavelengths.
Now there's an app from dgApps to convert between them all.
The app features a sliding fader to dynamically change frequency, wavelength and musical note, with locks to step through standard third octave frequencies or whole musical notes.
There's a built in oscillator so you can hear the frequency, and a frequency tracker so the app can tell you the frequency. Both the oscillator and the frequency tracker display the audio waveform.
A settings section allows for different tuning standards, and variations in the speed of sound. Lambda can also receive calculated Speed of Sound in Air values from another dgApps app, Cair. Lambda is now a universal app, equally at home on an iPhone as on an iPad. In Split Mode on an iPad device, side by side with Cair, the calculated Speed of Sound in Air is passed in real time to the Lambda app.
Lambda allows you to share frequency/wavelength/note data via all the usual sharing methods.