ReSlice - Slice your audio with an advanced, rhythmic arpeggiator and FX.
Typatone - Make music while you write
cassini - Polyphonic Synthesizer for iPhone/iPod touch
Frettable - Play your instrument and AI will write the sheet music
nlog Synth - Professional Virtual Analogue Synthesizer ::: check nlogmusic at YouTube :::
Tab Lab - Read and write music notation and tablature, together.