Virtual Audio Cable - Ever wanted to record your speaker output? (loopback) This is for you.
VB-Audio Virtual Cable - Connect Audio Applications together with a Virtual Audio Device
Loopback by RogueAmoeba - Get all the power of a high-end studio mixing board, right inside your Mac!
VAcard - [NOTE: You can download the application from ...
JACK Audio Connection Kit - JACK Audio Connection Kit|Home
SoundDesk Virtual Devices by LoudLab - SoundDesk Virtual Devices - Software devices to route audio across macOS.