ShiroKuro It's free. The free version will say it's demo, so some keys may be disabled, and the keyboard sound will be disabled after some time. In reality, non of those limitations cause any problem for casual use. If you use it long enough (> 30 minutes, I believe) in one session, you may need to close the app and relaunch it.
It's the same with the desktop version of Pianoteq, too.