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.
Sound Control - App-specific volume control
Loopback by RogueAmoeba - Get all the power of a high-end studio mixing board, right inside your Mac!
Power mixer - Power Mixer is a complete Windows volume control replacement.
JACK Audio Connection Kit - JACK Audio Connection Kit|Home