I keep meaning to try out one of these isomorphic keyboard apps and this one looks good. Here’s a little description:
Musix is a fully-customizable multiple-layout isomorphic musical keyboard for the iPad. Each hexagon on the screen is a note, and surrounding hexagons are harmonically related. Songwriters benefit by discovering new melodies and musical relationships. Novices find it easy to learn to play. Experienced musicians are rewarded with an intuitive interface. Shiverware presents Musix: the definitive isomorphic keyboard. For beginners, for experts, for you!