EarTrumpet - Volume Control for Windows
JACK Audio Connection Kit - JACK Audio Connection Kit|Home
Volume2 - Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control.
Virtual Audio Cable - Ever wanted to record your speaker output? (loopback) This is for you.
Volumouse - From authors website:
Loopback by RogueAmoeba - Get all the power of a high-end studio mixing board, right inside your Mac!