Sound Control - App-specific volume control
Flowkey - The easiest way to learn piano with your iPhone or iPad
Volume2 - Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control.
Yousician - Learn to play music at home, at your own pace
EarTrumpet - Volume Control for Windows
Melodics - Melodics is a desktop app that teaches you to play MIDI keyboards, pad controllers, and drums.