Following the announcement of the iM2 Tascam have put the app on the store and you don’t need the iM2 to use it either!
Oh yes, and it’s free!
Here’s the app’s description:
TASCAM PCM Recorder is a free stereo recorder for iOS devices. It supports up to 12 hours of recording, using the built-in microphone or connected USB devices like the TASCAM iM2 stereo microphone. EQ, limiting, Soundcloud support and more make this a full-featured professional recorder.