Soundflower
Free
Inter-application Audio Routing Utility for macOS
Soundflower is an open source kernel extension for macOS,
designed to create a virtual audio output device that can also act as an
input.
Allows applications to pass audio to other applications

Soundflower Setup on Logic
Soundflower is a
macOS system extension that allows applications to pass
audio to other applications. Soundflower is easy to use, it simply
presents itself as an audio device, allowing any audio application to
send and receive audio with no other support needed. Soundflower is
free, open-source, and runs on Mac Intel and PPC computers.
Example 1: To send audio from iTunes to Max/MSP, open the System
Preferences and select Soundflower (2ch) as the device for sound output
inside the Sound panel. Then, inside Max/MSP's DSP Status Window, select
Core Soundflower (2ch) as the input device. All output of iTunes should
now be sent to Max/MSP's adc~ object.
Example 2:
How to setup Garage Band,
Sound-flower, IAC, VFX
Soundflower-1.6.6b.dmg
Soundflower 1.6.6 Installer (includes SoundflowerBed) -- Use this for
OS 10.6 - OS 10.8 - 179.75KB