Synthesia 0.7.0 runs on Windows XP, Vista, or 7 as well as Mac OS X 10.4 or later. Download from the boxes below and enjoy! After you you play the game for a while, you may want to consider unlocking the built-in Learning Pack to add a few more educational features.
I downloaded the free version and I tried to play one of the many [over 160] pre-installed songs.

I scored 0 before giving up.

The falling coloured bars above the keyboard indicate which keys you should be playing by the time the bars actually reach the keyboard. You have a choice of instruments: Acoustic Grand Piano 39 notes or Acoustic Grand Piano 75 notes.

There are several other options to choose from before beginning to play or play automatically.

Link: Synthesia, Piano for Everyone