iAno (native Pianist) -

Pianist is a virtual piano for the iPhone and iPod Touch. Use it as a musical scratchpad when away from the studio, or as an instrument to jam with your friends.

A complete 88 key piano keyboard.
Each note sampled from a real piano for maximum realism.
Multi-touch. Up to 5 keys can be pressed at once allowing complex chords.
Animated piano keys react to your touch.
Scroll up and down the piano keyboard by octaves or individual keys.
Virtual "Soft" and "Sustain" pedals.
Multi-track recording. Duet with yourself.
Erase any mistakes, then go back and overdub replacement notes onto the track.
A configurable metronome can be enabled during recording.
Piano keys can be optionally labeled ("A3" etc) to aid those new to the instrument.

Text and screenshots are not enough to fully describe a product as dynamic as Pianist. The following video showcases some of the demos that ship with the application, and the quality of music that you can produce from an iPhone.