The Free Software Song is a filk song by Richard M. Stallman about free software. The song is set to the melody of the Bulgarian "Sadi Moma". This song is used by both Stallman's supporters and critics to support their positions. Jamie Zawinski has used this song as an explanation for why he thinks co-operation with Stallman is impossible. [1] A version of this song is also performed by a band (the GNU/Stallmans) during the credits of the documentary Revolution OS. Jono Bacon also recorded a heavy metal version of the song, and Fenster recorded a rhythmic version.