Apps with 'Connecting audio streams' feature
Sophisticated real-time, low latency routing of audio and MIDI data between apps.
Soundflower is a Mac OS X system extension that allows applications to pass audio to other applications.
Connect Audio Applications together with a Virtual Audio Device.
Virtual Audio Cable is the definitive audio routing tool for Windows that lets you redirect audio streams between applications and devices on your computer.
macOS software for taking the sound from applications and audio input devices and using them as inputs for anything else.
SoundDesk is the easiest way to turn your macOS into a professional mixing desk.
SoundDesk Devices are virtual connectors that you can use to route audio across apps.