Virtual Audio Cable - Ever wanted to record your speaker output? (loopback) This is for you.
Loopback by RogueAmoeba - Get all the power of a high-end studio mixing board, right inside your Mac!
JACK Audio Connection Kit - JACK Audio Connection Kit|Home
Dante Virtual Soundcard - Dante Virtual Soundcard turns your computer into a Dante-powered workstation, seamlessly...
VB-Audio Virtual Cable - Connect Audio Applications together with a Virtual Audio Device
AudioBus - With Audiobus, the revolutionary new inter-app audio routing system, you can connect your...