This app started with a small daily annoyance. I'd be on a call while music played in the background, and macOS only gave me one volume knob for everything. If I wanted the music quieter, the call got quieter too. If I wanted the call on my speakers and Spotify in my headphones, I was out of luck. Windows has had a per-app mixer for years, and the Mac options I found needed a kernel-level audio driver or a paid license. So I built one. Still uses Core Audio process taps to capture each app's audio, apply my volume, and play it back through whichever device I choose. There's no installed driver, no network access, and nothing is recorded. The hardest part was the realtime render callback, which I wrote in C++ so it never allocates memory or takes a lock. A single hiccup there comes out as an audible click.

Still

Every app gets it's own volume

Every app gets it's own volume