The Yamaha Tenori-on, Wikipedia (video) –

The Yamaha Tenori-on is an electronic musical instrument designed and created by the Japanese artist Toshio Iwai and Yu Nishibori of the Music and Human Interface Group at the YamahaCenter for Advanced Sound Technology. It consists of a hand-held screen in which a sixteen-by-sixteen grid of LED switches are held within a magnesium plastic frame. Any of these switches may be activated in a number of different ways to create sounds. Two built-in speakers are located on the top of the frame, as well as a dial and buttons that control the type of sound and beats per minute produced.

There’s an iOS version (not available in the US store it seems). Video above –

The iOS version of the world-renowned TENORI-ON brings you a completely new musical interface.
Even if you don’t know much about music, you can create music intuitively as if you were arranging sounds in space. The music that you see on the 16 × 16 grid of buttons is the music that is performed.
On the 16 × 16 grid of buttons, basically, the horizontal direction is time, and the vertical direction is pitch.By laying sounds on these buttons, you can combine rhythms and melodies to produce music. A button will glow when its sound is produced. The movements of the glowing lights produce a visual performance.

Learn more.

More:
TENORI-ON videos on YouTube.

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