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After Audio Hijack, Loopback was the second audio app I bought from Rogue Amoeba and I've used it almost constantly since. The beautiful thing about Loopback is that it just works - you set it, and then you can forget about it.
Loopback
Cable free audio routing for Mac
Farrago is new soundboard app for Mac, designed for lightning fast playback of audio. Whether it's musical accompaniment, sound effects, or anything else, Farrago puts your audio at your fingertips. It's great for podcasters, theater techs, and all manner of live performances.
Farrago
Robust, rapid-fire soundboards for Mac
SoundSource 3.0
The sound control that should be built into MacOS
Airfoil 5
Stream any audio from your Mac all around your network