Volume2 - Volume2 is an advanced Windows audio mixer, a complete replacement for the standard Volume Control.
Voicemeeter - Audio Processing and Audio Programming by V.Burel
Sound Control - App-specific volume control
Virtual Audio Cable - Ever wanted to record your speaker output? (loopback) This is for you.
Power mixer - Power Mixer is a complete Windows volume control replacement.
JACK Audio Connection Kit - JACK Audio Connection Kit|Home