Phonascus: A free opensource program to learn Music

Phonascus is a totally free program for studying music theory that allows you to focus on specific skills and exercises, on both theory and aural training. The different activities can be customized to meet your needs. Phonascus allows you to work at your own pace, providing interactive feedback until mastery of each concept is achieved.
Phonascus has no commercial purpose and, so, it is licensed under the GNU General Public License, meaning you can use it for free and that you have the right to access the source code and modify it if you like. No cost for you and no time wasted on garbage like registration codes, copy protection or advertisements.

http://www.lenmus.org/en/phonascus/downloads