JACK is a professional sound server daemon that provides real-time low latency connections for both audio and MIDI data between applications that implement its API. The API can be used through either JACK1 or JACK2.
JACK Audio Connection Kit vs Loopback opinions
super lite and opensource, also paying attention to latnecy
Soundflower is a Mac OS X system extension that allows applications to pass audio to other applications. Soundflower is easy to use, it simply presents itself as an audio device, allowing any audio application to send and receive audio with no other support needed.Discontinued
The project seems no longer developed. Last version, 2.0b2, released in December 2014, can be still downloaded from GitHub.
Soundflower vs Loopback opinions
At least it's free, and works extremely well for streaming. Sadly I can't hear my output without a multi-output device.
Soundflower offers extremely similar functionality to Loopback, including audio passthrough, audio stream connecting, and recording. It is also free and open source.
BlackHole is a modern macOS virtual audio driver that allows applications to pass audio to other applications with zero additional latency.
BlackHole Audio Loopback Driver vs Loopback opinions
It doents have an interface
Synchronous Audio Router is a software-based audio routing driver for Windows. You can create any number of Windows audio endpoints, either playback or recording, and route them using any digital audio workstation software which supports ASIO, all with low latency.Discontinued
The last version (0.13.1) was released in April 2018. Many issues in the repository going unanswered.