From Black Cat Systems:
Want to monitor PSK31 transmissions, without using a bulky computer? PSK31 lets you view ham radio PSK31 transmissions on your iPad. Just set your iPad next to your radio, tune in a PSK31 frequency, and watch the decoded text. There's a waterfall display of the audio spectrum, showing all of the PSK31 transmission. Tap on a signal, and PSK31 tunes into that transmission. Get your copy of PSK31 right now, and start decoding and displaying PSK31 transmissions in minutes.