MarcMoerd3o lets you play the mid three octaves (c - c, midi notes 48 - 84) of Ariaan Hogendijks Marcussen/Moerdijk pipe organ sampleset on up to three MIDI keyboards and a MIDI pedal connected to your iPad (2 or later) or iPhone (iPhone 5 or later is recommended).
Attention: This app is quite large (about 2 GB).