Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Synthesia - A fun way to learn how to play the piano.
Spek - Spek helps to analyse your audio files by showing their spectrogram.
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.
SoX - Sound eXchange is a command line utility that can convert various formats of computer audio files...
Playground Sessions - Online piano learning game.