<a href="https://en.wikipedia.org/wiki/Free_Software_Song" class="extiw" title="en:Free Software Song">Free Software Song</a>, an improvised piano version by Markus Haist.
Markus Haist. The original tune is that of <a href="https://en.wikipedia.org/wiki/Sadi_Moma" class="extiw" title="en:Sadi Moma">Sadi Moma</a>, a Bulgarian folk song.
GPLv3
<a rel="nofollow" class="external free" href="http://www.gnu.org/music/free-software-song.html">http://www.gnu.org/music/free-software-song.html</a>