It's a vanilla loopback Audio Server Plugin implementation, which is a userspace audio driver mechanism on macOS. Soundflower is an actual kernel-space driver u

It's a vanilla loopback Audio Server Plugin implementation, which is a userspace audio driver mechanism on macOS. Soundflower is an actual kernel-space driver using IOKit, which is the older (and deprecated) way of achieving the same thing. The actual work is done in a few dozen lines of code (see BlackHole_DoIOOperation at https://github.com/ExistentialAudio/BlackHole/blob/master/BlackHole/BlackHole.c#L3753 https://github.com/ExistentialAudio/BlackHole/blob/master/Bl...). The rest is just setting up the object model for the OS to provide metadata about the device.