The DX7 piano app is a free Android app with a MIDI controller. It has a lot of knobs for different effects that can be transmitter through the phone's micro USB to a MIDI input via a cable. You can also connect it to your computer. You have 24 keys you can use, from C5 to B7. The effects are: size, density, decay, damp, delay time, feedback, mix and delay mix. The great thing is that all the effects have the numbers showing their setting right below them. The app also has a screen to show delay time, a pitch bend, a wheel and two buttons to enable reverb and delay. It also indicated the voice you are using and its algorithm, as well as if any MIDI event is taking place. The app is best usable on a tablet screen of at least 8" just like any app with a playable keyboard. The app is great when you have no fizical controller near you, but to use it any where near the way you should, you have got to have a 10" tablet with a really good touch-screen. The DX7 app itself works great, even if it only has a pre-installed voice, the electric keyboard.