MiniPiano app is just that

MiniPiano is the light-weight, free version of popular piano app Finger Piano, from developer JYProduct. Like its older, more mature brother, it’s controlled by striking the keys on a virtual piano. But that’s pretty much where the similarities end.
As a matter of fact, that’s pretty much where Mini Piano ends: It’s a tiny, one-octave (plus a bonus semi-tone) piano without features like configuration or recording.
If you’re simply looking for a way to let out some creativity on the go, than Mini Piano is just right for you. However, if you’re looking for a little more, take a look at its sibling Finger Piano, for $2.99.