Voxal - Modify your voice in any application that uses a microphone. From girl to alien, the voice options for online video games, avatars and podcasts are limitless.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Autotalent - To make music
TwistedWave - TwistedWave is one of the unique audio editors that allow you to edit your music file online without any installation.
FL Studio - Image-Line's FL Studio, now on it's 12th version, is a well-known music production suite and the most popular beat processor on the market, due no doubt to its longevity. Read more about FL Studio.
Reason - Reason is a program that you can use to create music.