TonePad (App Store link) is a free iPhone app that’s a bit like musical crack.
It’s a matrix synthesizer/sequencer, derived from the design of the Yamaha Tenori On, via Andre Michelle’s ToneMatrix, letting you create musical phrases by pressing virtual “buttons”.
TonePad features a clean minimalist user interface with a full 16×16 matrix. The sound quality remains excellent regardless of how many notes are playing at the same time. You can save an unlimited number of songs.
The current song is also saved automatically on exit. Sharing your musical creations couldn’t be simpler.
You simply press the Upload button and give your friend the song code. Your friend then downloads the song directly into TonePad by pressing the Download button and entering that code.
Use headphones for best sound.