Free audio software programs for Windows, Mac and Linux
1. Recording and editing software
Audacity:
http://audacity.sourceforge.net/
Traverso:
http://traverso-daw.org/download.html
Frinika:
http://sourceforge.net/projects/frinika/
2. Audio processing software
Supercollider:
http://supercollider.sourceforge.net/
3. Music notation and score editor
MuseScore:
http://musescore.org/en/download
Canorus:
http://sourceforge.net/projects/canorus/