Download of XKeyPiano 1.1.1 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The application is included in Audio & Video Tools. We recommend checking the downloaded files with any free antivirus. The actual developer of this free software for Mac is CME.
From the developer:
XKeyPiano is a free app that turns your Mac into a real piano. The program requires a CME Xkey keyboard to make the most of your user experience. Xkey is a thin and beautiful USB MIDI keyboard with 25 or 37 full-size keys, made for amateur or professional musicians. If you don’t have any, you can still play around and have fun on your Mac only.
You may want to check out more Mac applications, such as CROSS-DJ, FuzzMeasure or FretPet, which might be related to XKeyPiano.