Someone finally came up with a Soundflower replacement, and it's free for Mac users | MusicRadar
Microsoft Apps
Audio Router - Open-Source Windows App
GitHub - wolfreak99/audio-router: Updated Fork of the now abandoned audiorouterdev/audio-router. Need help maintaining, please feel free to contribute.
Audio Router routes audio from programs to different audio devices
audiorouterdev · GitHub
GitHub - ExistentialAudio/BlackHole: BlackHole is a modern macOS virtual audio driver that allows applications to pass audio to other applications with zero additional latency.
Audio | Android Open Source Project
GitHub - ShortDevelopment/VB-Audio-Router: Advanced audio routing application build with UWP and the WinRT Audio Graph API