BestPractice is an excellent way to hear and learn music by slowing down or speeding up music on an MP3 file or even directly from a CD.
As you know, if you slow down or speed up music, it will often be distorted or sound unusual in some way. BestPractice attempts to correct any of this so that it keeps the original pitch when you hear it.
There are many reasons to want to do this. The first one that comes to mind is to learn individual parts by slowing down and hearing the right sound so you can play it on your favorite instrument.
The interface is very easy to use. You can choose your drive, or wherever the music is you want to load. From there you can play, pause, reverse and forward much like any multimedia player.
Then come all the fun options. You can adjust the playing pitch, pitch fine adjust and the playing speed as well as a few other related settings. From here you can also jump to a set time and even set what and when to loop if you want to hear it over and over again.
BestPractice has competition, but most of those require buying the application. This one is Open Source and gets the job done.