Voicemeeter - Audio Processing and Audio Programming by V.Burel
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
JACK Audio Connection Kit - JACK Audio Connection Kit|Home
Volume Scroll - Volume Scroll lets you control your main volume by hovering with your mouse cursor over the top...