How to get a Fritzbox to play music

In one afternoon - in almost 200 lines of script code and with telnet you can tell your Fritzbox how to play the piano with its LEDs.

This shows my Fritzbox router blinking an old German song for children:

You could play with so many things if you know how.

Caution: This mod was performed by unprofessional persons, please don't attempt to do this if you don't know what to do. If you know it, don't do it :)