http://touchpianist.com/ by Batuhan Bozkurt Touch Pianist is a musical toy / instrument that allows the user to perform hard-to-play classical piano music favorites (from composers like Beethoven, Mozart, Bach, Satie, Debussy to name a few) just by tapping the rhythm of the piece's particular sound events on a computer keyboard or a touch screen. It also provides live visualisation of the pieces that are being performed. There is no score keeping, the user is free to perform the music in any way they wish. The premise is that it is really fun to perform a piece you know well, exactly like you feel it with so little effort.
hi there! here is another instrument .Circuli is a generative ambient sound creator / instrument. You can play with it online and/or get it for your iOS device. Check the links above.
If you like Circuli, you may also want to see Otomata if you haven't already: